Acta Physica Polonica A
   




   Vol. 97
   No 5
   May 2000






	



 

MAGNETOELECTRIC EFFECT OF Cr2O3

Z. Latacz
Institute of Physics, Jagiellonian University, Kraków, Poland

A formula for the temperature dependent magnetoelectric susceptibility
of Cr2O3 is obtained using the method of renormalized spin waves of Nagai
and compared with the formula in random phase approximation. The three
coefficients ag, aLS, and aJ which respectively represent the change in
the g-factor, in the crystal field splitting and in the exchange integral
due to the electric field parallel to the easy axis, are determined by comparing
the theoretical with experimental susceptibility curves, as well as the
antiferromagnetic resonance shift.
 
PACS numbers: 75.80.+q, 75.50.Ee




 
119Sn HYPERFINE FIELDS IN RMn6Sn6 (R = Mg, Zr, Hf). EXPERIMENTAL
AND THEORETICAL STUDY

T. Mazeta, J. Tobolab, G. Venturinia 
and B. Malamana
a Laboratoire de Chimie du Solide Minéral Université Henri
Poincaré-Nancy I, associé au CNRS, UMR 7555 B.P. 239, 54506 Vandoeuvre
les Nancy Cedex, France 
b Faculty of Physics and Nuclear Techniques,
Academy
of Mining and Metallurgy Al. Mickiewicza 30, 30-059 Kraków, Poland

We performed both 119Sn Möossbauer experiments and electronic
structure calculations using the Korringa-Kohn-Rostoker method on the
hexagonal RMn6Sn6 (R = Mg, Zr, and Hf) compounds. According to previous
neutron diffraction results two types of commensurate magnetic order are
investigated: ferromagnetic for R = Mg and antiferromagnetic for R = Zr and
Hf. From 119Sn Möossbauer measurements, high transferred hyperfine
fields
on the tin nuclei are observed. The Hhf values are well supported by
the Korringa-Kohn- Rostoker results. Moreover, the calculated µMn
are in good agreement with the neutron diffraction data. When observing the
density of states, ZrMn6Sn6 is found near semimetallic 
limit.
 
PACS numbers: 76.60.Jx, 76.30.Lh, 71.15.Mb, 75.20.En




 
INFLUENCE OF ANNEALING TREATMENT ON THE STRUCTURE AND MAGNETIC
PROPERTIES OF Fe-Al-Cu-Nb-Si-B ALLOYS

G. Pavlik, P. Matta, P. Sovįk, A. Zorkovskį and 
M. Konc
Faculty of Science, P.J. Safįrik University, Park Angelinum 9, 041 54
Kosice, Slovakia

In this paper we present experimental results on influence of Al
content on the structure and saturation magnetostriction of Fe-Al-Cu-Nb-Si-B
alloys after heat treatment. Transmission electron microscopy observations
confirmed the existence of nanocrystalline structure after annealing at
490oC and 550oC for all samples. The crystallization temperature
of
FeSi phase and the temperature at which the polycrystalline transformation
starts were determined from temperature dependence of electrical
resistivity.
Aluminium slightly decreases the first crystallization temperature and
considerably decreases the saturation magnetostriction in as-quenched
state.
 
PACS numbers: 61.16.Bg, 75.50.Kj, 75.80.+q, 81.40.Rs



 
THE RESISTIVITY AND HALL EFFECT OF THE AMORPHOUS Cox
Ni70-xFe5Si15B10 RIBBONS

K. Perzyńskaa, M. Biernackaa, 
L. Dobrzyńskia,b, A. Malinowskia,
S. Tarasenkoa and P. Zaleskia
a Institute of Physics, 
University at Bialystok, Lipowa 41, 15-424
Bialystok, Poland 

b Soltan Institute for Nuclear Studies, 05-400
Otwock-Swierk, Poland

The influence of structural disorder and magnetism on the resistivity
of the amorphous CoxNi70-x
Fe5Si15B10 ribbons was
investigated.
The resistivity vs. alloy composition shows parabolic-like behaviour. In the
thermal behaviour, resistivities of the samples show apparent magnetic
contribution. They also exhibit minima at temperatures which can be
correlated with the Curie temperatures. Above T >= 0.5TC resistivity
increases linearly with increasing temperature. This effect is seemingly due
to electron-phonon scattering. Obviously, the chemical and positional
disorder is responsible for the major part of resistivity.
 
PACS numbers: 72.15.Cz



 
STRAINED TETRAGONAL BAIN PATHS IN Fe3Pt INVAR

M. Pugaczowa-Michalska and S. Lipiński
Institute of Molecular 
Physics, Polish Academy of Sciences Smoluchowskiego
17, 60-179 Poznań, Poland

Employing the LMTO-ASA method we calculated the total energy
variation
of Fe3Pt along the tetragonal distortion path connecting fcc and bcc
structures for isotropic biaxial path and uniaxially strained path and
compare the results with energies for the unstrained path.
 
PACS numbers: 75.50.Bb, 81.30.Kf


 

RELAXATION OF 53Cr SPIN ECHO SIGNALS IN 
Cd0.985Ag0.015Cr2Se4

G.N. Abelyasheva, V.N. Berzhanskya, 
S.N. Polulyakha and N.A. Sergeevb
a Department of Physics, 
Simferopol University Yaltinskaja 4, 333007
Simferopol, Ukraine 

b Institute of Physics, University of Szczecin,
Wielkopolska 15, 70-451 Szczecin, Poland

The frequency dependences of the relaxation times of NMR spin echo
signals of quadrupole nuclei 53Cr at te=tau and te=3tau 
in ferromagnetic semiconductor Cd0.985Ag0.015Cr2Se4 were
investigated at temperature 4.2 K. It was shown that there are two kinds of
the quadrupole nuclei 53Cr, which have quite different relaxation
times.
The existence of two kinds of the nuclei 53Cr was connected with doping
of the cadmium selenochromite with Ag+ ions.
 
PACS numbers: 76.20.+q, 76.60.-k, 76.60.Lz



 
57Fe HYPERFINE FIELD ANISOTROPY IN FERRITES AND ITS RELATION TO THE
NON-UNIFORMITY OF THE IONIC SURROUNDING

H. Stepįnkovį, J. Englich and J. Kohout
Faculty of 
Mathematics and Physics, Charles University V Holesovickįch 2, 
180 00 Prague 8, Czech Republic

The hyperfine field anisotropy tensors, obtained from analysis of
57Fe NMR spectra for iron sites in various magnetic oxides (barium
hexaferrite, lithium spinel, magnetite and yttrium-iron garnet) were used to
investigate the relation between the hf anisotropy and surrounding ionic
arrangement. While a reasonable correlation has been found when the
distribution of the nearest cations was considered, no correlation was
obtained between the hyperfine field anisotropy and the positions of the
nearest oxygen anions.
 
PACS numbers: 76.60.-k, 75.50.Gg



 

THE ELECTRONIC STRUCTURE OF THE RMn2Ge2 (R = Ca, Y, La, Ba)
ANTIFERROMAGNETS

J. Tobolaa, B. Malamanb and G. Venturinib
a Faculty 
of Physics and Nuclear Techniques, Academy of Mining and
Metallurgy Al. Mickiewicza 30, 30-059 Kraków, Poland 

b Laboratoire de
Chimie du Solide Mineral, Université Henri Poincaré-Nancy I, 54506
Vandoeuvre les Nancy Cedex, France

The electronic structure of the tetragonal RMn2Ge2 (R = Ca, Y, La,
Ba) antiferromagnets is presented using the self-consistent
Korringa-Kohn-Rostoker method. According to the neutron refinements, two
types of collinear antiferromagnetic structure are taken into account: AF1
for YMn2Ge2 and AF2 for the other compounds. The calculated magnetic
moments on Mn: 2.17µB (YMn2Ge2), 2.84 
µB (CaMn2Ge2), 2.95
µB (LaMn2Ge2), and 3.47 µB 
(BaMn2Ge2) remain in good
agreement with the neutron data (in µB) 2.20, 2.67, 3.05, and 3.66,
respectively. As seen on antiferromagnetic density of states, all systems
are
metallic, however BaMn2Ge2 is found near semimetallic limit. The total
energy Korringa-Kohn-Rostoker computations on CaMn2Ge2,
performed in both antiferromagnetic phases, result in preferring of the AF
2 structure.
 
PACS numbers: 71.15.Mb, 71.15.Nc, 75.20.En, 75.20.Hr, 75.50.Ee




 

CRYSTAL-FIELD ORIGIN OF THE GIANT MAGNETOCRYSTALLINE ANISOTROPY OF
PrRu2Si2

R. Michalskia,b, Z. Ropkab 
and R.J. Radwańskia, b
a Institute of Physics, 
Pedagogical University Podchorazych 2, 30-084
Kraków, Poland 

b Center for Solid State Physics, sw. Filip 5, 31-150
Kraków, Poland

PrRu2Si2 shows ferromagnetism below 14 K with the ordered moment of
2.7µB. It exhibits an enormous magnetic anisotropy at 4.2 K with the
anisotropy field of about 400 T. We have attrributed the magnetism of
PrRu2Si2 to the Pr3+ ions. Thus we performed calculations of
the fine electronic structure of the Pr3+ ion in the tetragonal symmetry,
relevant to PrRu2Si2, taking into account crystal-field and inter-site
exchange interactions. Our calculations reproduce well the zero-temperature
moment, the single-crystalline magnetization curves, and giant anisotropy
field as 400 T. The magnetocrystalline-anisotropy energy K1 of 59
J/cm3 is the largest known anisotropy - the anisotropy energy of the
Nd2Fe 14B supermagnet amounts to 12.5 J/cm3 only. 
Unfortunately, this giant anisotropy is confined to low temperatures only which prohibits its
technical applications in the permanent-magnet industry.
 
PACS numbers: 71.70.-d, 71.20.Eh



 
MAGNETIC ORDERING OF RAgSb2 COMPOUNDS

G. Andréa, F. Bouréea, M. Kolendab, 
B. Lesniewskac, A. Olesc and A. Szytulab
a Laboratoire 
Léon Brillouin (CEA-CNRS) CEN-Saclay 91191Gif-Sur-Yvette
Cedex, France 

b Institute of Physics, Jagiellonian University, Reymonta 4,
30-059 Kraków, Poland 

c Department of Physics and Nuclear Techniques,
Academy of Mining and Metallurgy Reymonta 19, 30-059 Kraków, Poland

The magnetic structures of the polycrystalline samples of
RAgSb2 (R=Ce, Pr, Nd, Tb-Tm) are determined. All compounds
crystallize in the tetragonal ZrCuSi2-type of crystal structure and
except
CeAgSb2 they are antiferromagnets with a Néel temperature of 11 K for 
R = Tb and 2 K for Tm. CeAgSb2 below TC=9.5 K is ferromagnet with the
magnetic moment equal to 0.33µB and parallel to c-axis. In NdAgSb2
the sine modulated magnetic ordering described by the wave vector k = (0.5435,0,0) is observed. 
Below TN a collinear antiferromagnetic
structure with the magnetic (a,a,2c) for R = Pr and (2a,a,c) for R = Tb, Dy,
Ho, and Er is observed. For Ho-compound with an increase in temperature the
coexistence of two structures is observed: commensurate collinear and
incommensurate sine modulated. In TmAgSb2 the coexistence of the two phases
is observed at T = 1.4 K. With an increase in temperature only the
incommensurate phase stays.
 
PACS numbers: 75.30.Cr, 75.30.Kz, 75.50.Ee



 
THE PHASE DIAGRAM OF THE SECOND-TYPE ANTIFERROMAGNET

T. Balcerzak and A. Radomska
Department of Solid State Physics, 
University of Lódz Pomorska 149/153,
90-236 Lódz, Poland

We investigate theoretically the phase diagrams of the second-type
antiferromagnet with the fcc structure. Besides the nearest-neighbour and
next-nearest-neighbour exchange interactions, the biquadratic and
long-range dipolar terms are taken into account. The results can be useful
to discuss the phase diagram of europium telluride under external 
pressure.
 
PACS numbers: 75.10.-b, 75.50.Ee, 75.50.Pp



 
CORRELATION BETWEEN MAGNETIC PHASES AND INSULATOR-METAL TRANSITION IN
La1/3Nd1/3Ca1/3MnO3 PEROVSKITE

J. Baszyńskiai, B. Idzikowskia, 
T. Tolińskia and A. Hoserb
a Institute 
of Molecular Physics, Polish Academy of Sciences Smoluchowskiego
17, 60-179 Poznań, Poland 

b Hahn-Meitner-Institut, Glienicker Strasse 100,
14109 Berlin, Germany

The La1/3Nd1/3Ca1/3MnO3 
ceramic perovskites are
investigated using the neutron diffraction technique and resistance
measurements in the temperature range from 260 K down to 5 K. We have found
that the integrated intensity of the antiferromagnetic peaks was growing
with
decreasing temperature and reached the maximum at a temperature about 20 K
lower than that of the semiconductor-metal transition and did not vanish at
5 K. The semiconductor-metal transition is correlated with the temperature
of the maximum of the lattice c-parameter and the percolation of
ferromagnetic domains. Our results suggest that although the ferromagnetic
long-range order is established through the semiconductor-metal transition
induced percolation network, locally the antiferromagnetic correlation can
remain.
 
PACS numbers: 71.30.+h, 75.25.+z



 

ELECTRONIC STRUCTURE AND ELECTRON-TRANSPORT PROPERTIES OF
(Gd1-xYx)2In COMPOUNDS

W. Borgiela and J. Deniszczykb
a Institute 
of Physics, Silesian University, Universytecka 4, 40-007
Katowice, Poland 

b Institute of Physics and Chemistry of Metals, Silesian
University Bankowa 12, 40-007 Katowice, Poland

Based on the electronic structure of the ferromagnetic Gd2In
and (Gd0.5 Y0.5)2In compounds the high-temperature magnetic
part of the electrical resistivity of (Gd1-xYx)2In as a function of Y
concentration was calculated and analyzed. The main interaction which causes
the finite magnetic part of the conductivity was assumed in a form of
stochastically distributed in space s-f interaction. The calculated
resistivity of (Gd1-xYx)2In alloys qualitatively reproduces the
experimental data.
 
PACS numbers: 72.10.-d, 72.15.-v, 71.20.Eh, 71.20.-b



 

LOW-FIELD MAGNETORESISTANCE IN MANGANITE THIN FILMS

E.S. Vlakhova,b, K. Döorra, 
K.-H. Müllera, A. Handsteina, K.
Nenkova,b*, T. Waltera, R.A. Chakalovc, 
R.I. Chakalovac and A.Y. Spasovc
a Institut für 
Festkörper- und Werkstofforschung Dresden P.O. Box
270016, 01171 Dresden, Germany 

b International Laboratory of High Magnetic
Fields and Low Temperatures Gajowicka 95, 53-529 Wroclaw, Poland

c Institute
of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria

Grain boundaries play an important role in low-field magnetoresistance
of La0.7Ca0.3MnO3 and 
La0.7Sr0.3MnO3 thin films
deposited by magnetron sputtering and pulsed laser deposition on YSZ(100)
and silicon substrates buffered by YSZ. Well-pronounced low-field
magnetoresistance hysteresis was observed in magnetic fields applied in
in-plane and out-of-plane directions. High values of local magnetoresistance
sensitivity d(MR)/dH in the vicinity of the coercive field were obtained
reaching up to 0.2%/Oe for La0.7Ca0.3MnO3 
samples at 5 K.
 
PACS numbers: 75.70.Ak, 73.50.Dn



 

GIANT MAGNETORESISTANCE IN MELT-SPUN Co-Cu MODIFIED BY RARE EARTHS

B. Idzikowskia,b, U.K. Rösslera, 
A. Handsteina, K. Nenkova and
K.-H. Müllera
a Institut für 
Festkörper- und Werkstofforschung Dresden P.O. Box
270016, 01171 Dresden, Germany 

b Institute of Molecular Physics, Polish
Academy of Sciences M. Smoluchowskiego 17, 60-179 Poznań, Poland

Samples of the composition RExCo20Cu80-x, 
RE = Sm, Gd or Dy
(x = 0, 1, and 3) were produced by melt-spinning and subsequent annealing. The
magnetoresistance is negative as in granular Co-Cu, but its values depend
on
the kind of rare earth element added and on changes in the microstructure
induced by thermal annealing. An addition of 1 at.% rare earth metal to
Co20Cu80 yields a considerable increase in the magnetoresistance
ratio,
whereas an addition of 3 at.% causes a decrease. E.g., by addition of 1
at.% Dy to Co20Cu80 and optimal thermal treatment, the value of
magnetoresistance ratio measured at 10 K in a field of 5 T increases from
-14% to -28%. The effect can be attributed to the presence of clusters
of
hexagonal Dy(Co,Cu)5, which was ascertained from X-ray diffraction data, or
other, metastable rare-earth compounds and paramagnetic rare-earth atoms in
the Cu matrix.
 
PACS numbers: 75.70.Pa, 75.50.Tt



 
POINT-CONTACT SPECTROSCOPY OF Ce1-xRExNi5 (RE = Pr, Nd)

T. Kacmįrovįa, M. Reiffersb, 
J. Garcia Soldevillac, J.C.
Goméz Salc, J.I. Espesoc and J.A. Blancod
a 
Faculty of Sciences, University of P.J. Safįrik Park Angelinum 9, 041
54 Kosice, Slovakia 

b Institute of Experimental Physics, Watsonova 47,
043 53 Kosice, Slovakia 

c CITYMAC, Facultad de Ciencias, Universidad de
Cantabria, 39005 Santander, Spain 

d Departamento de Fisica, Universidad de
Oviedo, 33007 Oviedo, Spain

We report on the study of the electron-quasiparticle interaction
function in Ce1-xREx Ni5 (RE = Pr, Nd) pseudobinary compounds for
x = 0, 0.2, 0.5, 0.8, and 1 measured by means of point-contact spectroscopy. The
measured point-contact spectra (d2V/dI2 - directly proportional to the
electron- quasiparticle interaction function) of the heterocontacts between
Ce1-x RExNi5 and Cu in the ballistic regime are presented.
 
PACS numbers: 73.40.Jn, 
71.70.Ch, 71.70.Gm



 
ELECTRICAL CONDUCTIVITY FOR THE STRONGLY CORRELATED AND HYBRIDIZED
HUBBARD BAND

R. Kosimowa, W. Borgiela and J. Deniszczykb
a Institute 
of Physics, Silesian University Universytecka 4, 40-007
Katowice, Poland 

b Institute of Physics and Chemistry of Metals, Silesian
University Bankowa 12, 40-007 Katowice, Poland

The magnetic and electrical transport properties of strongly
correlated
Hubbard band (f-band) hybridizing with the non-correlated conduction band
(c-band) was studied. The many-body model Hamiltonian was treated within the
modified alloy analogy scheme and the resulting one-body problem was solved
with the use of coherent potential approximation. Within the
Kubo-Greenwood
formalism the dc electrical conductivity for bcc magnetic system was
calculated and its variation with temperature and number of electrons was
examined for different values of the Coulomb and hybridization (V) coupling
constants. We found that the effect of strong correlations and hybridization
on the conductivity is similar to that produced by the scattering due to the
s-f interaction (spin disorder resistivity).
 
PACS numbers: 71.10.Fd, 71.27.+a, 72.10.-d, 72.15.-v



 
ELECTRONIC, MAGNETIC AND TRANSPORT PROPERTIES OF YCo3 B2 COMPOUND

A. Kowalczyk, A. Jezierski, L. Smardz and J. Baszyński
Institute of
Molecular Physics, Polish Academy of Sciences Smoluchowskiego 17, 60-179
Poznań, Poland

We studied the electronic, magnetic and transport properties of the
hexagonal YCo3B2 compound. The electronic structure was studied by X-ray
photoemission spectroscopy and ab initio self-consistent tight binding
linear muffin tin orbital method. We found a good agreement between the
experimental X-ray photoemission spectroscopy valence band spectra and
theoretical calculations. Theoretical calculations showed that the 
YCo3B2
is a paramagnet in agreement with experimental results. Electrical
resistivity at low temperatures shows a T2 dependence, implying that the
scattering by the spin fluctuactions is dominant in this temperature 
range.
 
PACS numbers: 72.15.Eb, 75.20.En



 
KEr(MoO4)2 AND CsDy(MoO4)2 
- LOW-DIMENSIONAL ISING MAGNETS

M. Kacmįra, A. Orendįcovįa, 
E. Cizmįra, D.
Horvįtha, M. Orendįca, V. Bondarenkob, 
A.G. Andersb, A. Fehera
and M. Jascura
a Faculty of Science, 
P.J. Safįrik University, Park Angelinum 9, 04154
Kosice, Slovakia 

b Institute of Low Temp. Physics and Engineering Lenin
Avenue 47, 310164 Kharkov, Ukraine

In the present work the behaviour of cluster excitations in magnetic
field, B, parallel to the easy axis was experimentally studied by the
measurements of KEr(MoO4)2 and CsDy(MoO4)2 
specific heat, C, vs. B
dependence studied at a constant temperature. Corresponding Monte Carlo
simulations of C revealed that despite of the fact that the Ising
exchange-coupling models proved useful for a sufficient description of the
specific heat of these dipolar systems in B=0, the analysis of current
experimental data requires a partial renormalization of exchange-coupling
constants previously obtained from B=0 analysis. The influence of crystal
field effects and long-range character of spin correlations is 
discussed.
 
PACS numbers: 75.40.Cx, 75.10.Hk, 75.40.Mg



 
THE ANISOTROPY OF THE ELECTRICAL RESISTIVITY AND THERMAL EXPANSION OF
SINGLE CRYSTAL DyNi5

E. Kacmarcikovįa, M. Reiffersa, 
M. Mihįlika, J. Kovįca, A. Menovskyb, 
J. Garcia Soldevillac, A. Se nas Parientec and J.C.
Goméz Salc
a Institute of Experimental Physics, 
Watsonova 47, 043 53 Kosice, Slovakia 

b Van der Waals-Zeeman Institute, University of Amsterdam 1018 XE
Amsterdam, Netherland 

c CITYMAC, Facultad de Ciencias, Universidad de
Cantabria, 39005 Santander, Spain

The results of the measurements of temperature dependence of the
electrical resistivity rho(T), thermal expansion L(T) and susceptibility
chi(T) on single crystal DyNi5 in the temperature range 4.2-300 K are
reported. The maximum in rho(T) at TN=12.2 K was observed which
corresponds to the transition to antiferromagnetically ordered state. Taking
into account the Bloch-Grüneisen formula for electron-phonon
contribution
rhoph(T) to rho(T) the anisotropic magnetic contribution 
rhomag(T) was determined. We also observed the anisotropic behaviour of L(T)
at low temperatures.
 
PACS numbers: 72.15.Eb, 65.70.+y, 71.70.Gm



 
ELECTRONIC STRUCTURE AND TRANSPORT PROPERTIES OF UFe2 SYSTEM

A. Szlafereka, A. Szajeka, J. Baszyńskia, 
L. Smardza, A. Kowalczyka 
and M. Timkob
a Institute of Molecular Physics, Polish Academy 
of Sciences Smoluchowskiego 17, 60-179 Poznań, Poland 

b Institute of Experimental Physics, Slovak
Academy of Sciences Watsonova 47, 043 53 Kosice, Slovakia

The electronic structure of the UFe2 compound was studied by X-ray
photoemission spectroscopy and ab initio self-consistent tight binding
muffin tin orbital method. This compound crystallizes in a cubic Laves
phase.
The calculated valence band spectrum is characterized by two peaks due to
U(5f) and Fe(3d) states. We have found a good agreement between the
experimental valence band spectrum and theoretical ab initio
calculations. The carrier concentration estimated from the Hall effect
amounts to approx1022 cm-3.
 
PACS numbers: 71.15.La, 71.20.Lp, 72.15.Eb



 
MAGNETIC PROPERTIES OF RRhGe (R = Dy AND Tm) COMPOUNDS

W. Bazelaa, M. Hofmannb, S. Baranc, 
B. Pencc, A. Szytulac and A. Zygmuntd
a Institute 
of Physics, Technical University of Cracow Podchorazych 1,
30-084 Kraków, Poland 

b Berlin Neutron Scattering Centre, Hahn-Meitner
Institute, Berlin-Wannsee, Germany 

c Institute of Physics, Jagiellonian
University, Reymonta 4, 30-059 Kraków, Poland 

d W. Trzebiatowski Institute
of Low Temperatures and Structural Research Polish Academy of Sciences,
Okólna 2, 50-950 Wroclaw, Poland

The magnetic properties of the ternary intermetallic RRhGe (R = Dy and
Tm) were investigated by magnetic and neutron diffraction measurements.
These
compounds crystallize in a TiNiSi-type orthorhombic structure and are
antiferromagnets with the Néel temperature 20 K (R = Dy) and 6.2 K (R =
Tm). The neutron diffraction data reveal that the magnetic order in TmRhGe
is
collinear with the magnetic unit doubled along the b-axis respective to the
crystal one.
 
PACS numbers: 75.30.Cr, 75.30.Kz, 75.50.Ee



 
MAGNETIC BEHAVIOUR AND ELECTRONIC STRUCTURE OF THE R2 PdSi3 (R = Ce,
Nd, Tb-Er) COMPOUNDS

A. Szytulaa, M. Hofmannb, B. Penca, 
M. Slaskic, Subham Majumdard, E.V. Sampathkumarand 
and A. Zygmunte
a Institute of Physics, Jagiellonian 
University, Reymonta 4, 30-059 Kraków, Poland 

b Berlin Neutron Scattering Centre, Hahn-Meitner Institute 14109
Berlin-Wannsee, Germany 

c School of Physics and Space Research, University
of Birmingham, Birmingham, UK 

d Tata Institute of Fundamental Research Homi
Bhabha Road, Colaba, Mumbai 400005, India 

e W. Trzebiatowski Institute of
Low
Temperatures and Structural Research Polish Academy of Sciences, Okólna 2,
50-950 Wroclaw, Poland

The magnetic properties including the magnetic structure were
determined by magnetometric and neutron diffraction measurements of the
polycrystalline samples of R2 PdSi3 (R = Ce, Nd, Tb-Er). 
In Ce2PdSi3 the
Ce moments order below 2.5 K. The Nd magnetic moments in Nd2PdSi3 
exhibit
ferromagnetic ordering below 17 K. In Tb2PdSi3, a complex situation is
observed: in the temperature range from 1.5 K to (TN=25 K), there is a
coexistence of a ferromagnetic spiral (about 75% of the magnetic moment)
and
a spin-glass (about 25%). For the Dy, Ho, and Er compounds, below TN
(7.5, 8, and 7 K respectively), sinusoidally modulated structures are
observed. The valence band and the core level photoemissions of 4d of
rare-earth metal, 3d Pd, 2s and 2p Si were investigated by X-ray
photoemission spectroscopy measurements.
 
PACS numbers: 71.20.-b, 75.30.Cr, 75.30.Kz,
79.60.-i



 
TUNNELING CONDUCTIVITY OF MANGANITES WITH NEGATIVE MAGNETORESISTANCE

Yu.V. Medvedeva, V.Yu. Tarenkova, V.M. Svistunova, 
A.V. Abaloshevb,
I.S. Abaloshevab and S.J. Lewandowskib
a Donetsk 
Physical-Technical Institute of the National Academy of Sciences
of Ukraine R. Luxemburg 72, 340114 Donetsk, Ukraine 

b Instytut Fizyki PAN,
Al. Lotników 32/46, 02-668 Warszawa, Poland

Tunneling investigations of ferromagnetic La0.6Sr0.4MnO3
ceramic samples showing negative magnetoresistance effect were carried out
in two types of junctions: symmetric ``break junctions'' and asymmetric
ceramics-insulator-metal junctions. The results are consistent
with the presence of small ferromagnetic clusters in the insulating barriers
of both types of junctions and suggest a two-phase state realized by
impurity mechanism of phase separation.
 
PACS numbers: 75.70.Pa



 
NEUTRON DIFFRACTION STUDY OF FERROMAGNETIC ORDERING IN
La1/3Nd1/3Ca1/3MnO3 INDUCED BY ELECTRIC FIELD

J. Baszyńskia, B. Idzikowskia, T. Tolińskia 
and A. Hoserb
a Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego 17, 60-179 Poznań, Poland 

b Hahn-Meitner Institut, Glienicker Strasse 100,
14109 Berlin, Germany

We used the neutron diffraction technique to study the ferromagnetic
ordering process in La1/3Nd1/3Ca1/3MnO3 
induced by the short
impulse of the external electric field E=4 V/cm at a magnetic field H=1.5 T.
Our sample was prepared by the standard solid-state reaction. The
diffraction
measurements at 4 K, carried out for the neutron wavelength lambda=0.2442
nm, have revealed the orthorhombic perovskite structure with the unit-cell
parameters: a=0.5480 nm, b=0.5550 nm and c=0.7737 nm. We observed that a
short impulse of the electric field develops the ferromagnetic ordering in a
similar way as the magnetic field up to 4 T. We assume that the increased
ferromagnetic ordering induced by the external electric field at a given
magnetic field has the same physical origin as in the case of the Zener
double exchange. The effect is confirmed by magnetic moment measurements
using vibrating sample magnetometer.
 
PACS numbers: 71.30.+h, 75.25.+z




 
MAGNETIC PROPERTIES OF THORIUM FERRICYANIDE

R. Göbl, M. Zentkovį, V. Kavecansky, J. Kovįc and A.
Zentko
Institute of Experimental Physics, Slovak Academy of Sciences Watsonova 47,
043 53 Kosice, Slovakia

The magnetic properties of Th3[Fe(CN)6]·10H2O were
investigated.
It was shown that this compound is antiferromagnetically ordered in the low
temperature region. The observed antiferromagnetic ordering is stable only
in the low field.
 
PACS numbers: 75.30.Cr



 
MAGNETIC PROPERTIES OF LAYER-TYPE COMPOUNDS TlGdS2 AND TlGdSe2

M. Duczmal a, L. Pawlaka 
and S. Pokrzywnickib
a Wroclaw University of Technology, 
Department of Chemistry Wybrzeze Wyspiańskiego 27, 50-370 Wroclaw, Poland 

b Institute of Mathematics,
Physics and Chemistry, Technical University of Opole Luboszycka 7, 45-036
Opole, Poland}

Ternary thallium lanthanide dichalcogenides TlLnX2 (X = S, Se, or Te;
Ln = lanthanide, except Ce and Pr) crystallize in the rhombohedral structure
of alpha-NaFeO2 type (R3m). Their crystal lattice consists of the
layers of Ln3+ ions separated by three layers of the non-magnetic ions
(-Ln-X-Tl-X-Ln-). The magnetization was measured in the field range 0-14 T.
The molecular field constants lambdam were estimated by fitting the
Brillouin function to the experimental magnetization plots. The difference
between the lambdam values for the thallium gadolinium sulphide and the
selenide corresponds to the different character of Gd-S and Gd-Se bonds
and gives rise to the different J1 and J2 exchange 
integrals.
 
PACS numbers: 75.50.Ee, 75.30.Cr



 
ELECTRON TRANSPORT AND POINT CONTACT SPECTROSCOPY OF CUBIC DyCu5

K. Nenkova,b, B. Idzikowskia,c, S. Ilkovicd, 
E. Kacmarcikovįe, M. Reifferse 
and K.- H. Müllera
a Institut für Festkörper- und 
Werkstofforschung Dresden P.O. Box 270016, 01171 Dresden, Germany 

b International Laboratory of High Magnetic
Fields Gajowicka 95, 53-421 Wroclaw, Poland 

c Institute of Molecular
Physics, Polish Academy of Sciences Smoluchowskiego 17, 60-179 Poznań,
Poland 

d Faculty of Sciences, University of Presov 17. novembra 1, 080 78
Presov, Slovakia 

e Institute of Experimental Physics, Slovak Academy of
Sciences Watsonova 47, 043 53 Kosice, Slovakia

The electron transport properties and point contact spectra of
melt-spun DyCu5 with the cubic phase (structure type AuBe5, 
space group
F43m) were investigated. It was found by ac-susceptibility
measurements that below a transition temperature Tm=6.5 K this phase
shows metamagnetism. Between Tm and TC=14.5 K a spontaneous
magnetization is found. Our measurements of electrical resistivity confirm
the existence of two magnetic phase transitions in the compound.
Furthermore,
we present point contact spectra of DyCu5-Cu heterocontacts which are
directly proportional to the electron-quasiparticle interaction function.
Apart from a peak at about 18 meV, which is characteristic of electron-phonon 
interaction in pure Cu,
we observed a series of additional maxima at lower energy, which are
connected with the allowed 4f-transitions from the ground state to excited
crystalline electric field levels.
 
PACS numbers: 71.20.Eh, 72.15.Eb, 73.23.Ad, 73.40.Jn





 

MAGNETOCRYSTALLINE ANISOTROPY OF Tb1.1(FeCo)11 Ti

T.I. Ivanovaa, N.Yu. Pankratova, Yu.G. Pastushenkovb 
and K.P.Skokovb
a Physics Department, 
Moscow State University, 119899, Moscow, Russia

b Physics Department, Tver State University, 170000 Tver, Russia

The Tb1.1Fe11-xCoxTi (x = 0, 1, 2, 3, 4) compounds 
with the 
ThMn12-type structure were studied by using the torque and magnetization
measurements in order to investigate temperature and composition behavior of
the magnetocrystalline anisotropy. The Tb1.1(FeCo)11Ti single crystals
demonstrated spin reorientation transition from easy axis to easy plane with
the decrease in temperature. The substitution of Co for Fe produces an
enhancement of the Curie temperatures, decreases temperatures of spin
reorientation transition and appearance of canted 
structure.
 
PACS numbers: 75.60.Ch




 
SUSCEPTIBILITY BEHAVIOUR OF CuGeO3: COMPARISON BETWEEN EXPERIMENT AND
THE QUANTUM TRANSFER MATRIX APPROACH

M. Bieliński
Institute of Physics, Adam Mickiewicz University ul.
Umultowska 85, 61-614 Poznań, Poland

and J.-P. Renard
Institut d'Electronique Fondamentale, Université 
Paris-Sud Batiment 220, 91405 Orsay Cedex, France

Thermodynamical properties of one-dimensional S=1/2 Heisenberg model
with dimerized nearest- and uniform next-nearest-neighbour interactions are
studied by the numerically exact quantum transfer matrix method and the
results are applied to CuGeO3. Suzuki-Trotter formula is used to obtain a
classical system with spin sigma=3/2 and effective interactions between
nearest-neigbours only. Magnetic susceptibility curve is calculated and
compared with new experimental results performed in a wide temperature
range,
revealing the presence of frustration in the model proposed for 
CuGeO3.
 
PACS numbers: 75.10.Jm, 75.40.Cx, 75.40.Mg



 

GROUND-STATE ENERGY OF A FRUSTRATED ± J ISING MODEL ON A STRIP OF
SQUARES

M. Blaszyk and B. Fechner
Institute of Physics, 
A. Mickiewicz University Umultowska 85, 61-614
Poznań, Poland

We investigated a ± J Ising model on an infinite strip of squares of
the width of one and two bonds with a random distribution of ferro- and
antiferromagnetic exchange interactions. The exact ground-state energy as a
function of the concentration of antiferromagnetic bonds was derived and its
singular points in the complex-plane were found.
 
PACS numbers: 05.50.+q, 75.10.Nr, 75.50.Lk



 

MONTE CARLO SIMULATIONS OF THE ASHKIN-TELLER MODEL

L. Debski
Institute of Physics, Adam Mickiewicz University
Umultowska 85, 61-614 Poznań, Poland

Monte Carlo simulations are used to analyse the behaviour of the
extended Ashkin-Teller model in two (2D) and three (3D) dimensions from the
ratio of the square of the second moment of the order parameter to its
fourth
moment. The critical surface in three dimensional parameter space is
calculated in regions where the Ising transitions are expected both for the
ferro-and antiferromagnetic 
regions.
 
PACS numbers: 75.10.Hk, 75.40.Mg, 64.70.-p



 

MANIFESTATION OF SPIN-GLASS-LIKE BEHAVIOR IN THE ORGANOMETALLIC MAGNET

V.P. Dyakonova,c, M. Arciszewskaa, W. Dobrowolskia, 
A. Szewczyka,
H. Szymczaka, E. Aksymentievab, V. Varyukhinc, 
E. Zubovc and M.U. Gutowskaa
a Institute of Physics, 
Polish Academy of Sciences Al. Lotników 32/46,
02-668 Warszawa, Poland 

b Lviv State University, Lviv, Ukraine 

c Donetsk Physico-Technical Institute, Ukraine

Ac susceptibility (chiac) and dc magnetization (Mdc) of
the organometallic magnet Na[FeO6(C10H8N)3] 
have been studied in
temperature range of 4.2-200 K, in an external magnetic field up to 16 kOe.
Some peculiarities of the chiac and M dc behavior, which are
characteristic of spin-glasses, e.g. cusps in the susceptibility and
zero-field-cooled magnetization, an irreversibility between the field-cooled
and zero-field-cooled magnetization and dependences of the Tcusp
temperature on the frequency and the intensity of the magnetic field, were
observed at low temperatures.
 
PACS numbers: 75.30.Kz, 75.40.Cx



 

QUASICRITICAL BEHAVIOUR OF THE NMR AND µSR RELAXATION IN YMn2Dx

A. Paja, P. Mietniowski and H. Figiel
University of Mining and Metallurgy, 
Faculty of Physics and Nuclear
Techniques Department of Solid State Physics, Al. Mickiewicza 30, 30-059
Cracow, Poland

The magnetic and structural properties of YMn2 are strongly
influenced
by introduction of hydrogen (deuterium) in the structure, however, it only
slightly modifies the noncollinear antiferromagnetic structure of the
compound. The temperature dependences of the NMR relaxation times T1 and
T2
of deuterium and the zero-field relaxation of muons in YMn2Dx were
measured
at temperatures above the magnetic ordering temperature TN. The
corresponding relaxation rates are described by the empirical expression
(T/TN-1)-eta, where the exponent eta 
increases linearly with
deuterium concentration x. To explain this behaviour, the Moriya theory of
spin fluctuations was used. The expressions for NMR and µSR relaxation
rates have been calculated. The resultant formulae agree well with the
experiment, giving reasonable values of fitting parameters. The results
obtained are discussed in terms of spin fluctuation excitation 
spectrum.
 
PACS numbers: 75.40.-s, 76.60.-k, 76.75.+i




 

EFFECT OF HEAVY ION IRRADIATION ON THE MAGNETIC PROPERTIES OF CuGeO3

L. Gladczuka, E. Mosiniewicz-Szablewskaa, R. Szymczaka, 
M. Barana, H.A. Dabkowskab, J. Choińskic, 
T. Czosnykac and H. Szymczaka
a Institute of Physics, 
Polish Academy of Sciences Al. Lotników 32/46,
02-668 Warsaw, Poland 

b Brockhouse Institute for Materials Research,
McMaster
University, Hamilton, Canada 

c Heavy Ion Laboratory, Warsaw University,
Warsaw, Poland

The influence of heavy ion irradiation on the magnetic properties of
the spin-Peierls compound CuGeO3 has been investigated by means of the
electron paramagnetic resonance, the spontaneous magnetization, and the low
field ac susceptibility. The measurements were performed on the CuGeO3
single crystals before and after irradiation with 80 MeV oxygen ions in the
wide temperature range of 2-300 K. It was found that the irradiation
induced
an increase in the EPR signal intensity, magnetization, and susceptibility
of
this material. It was also shown that the irradiation does not lead to a
decrease in the spin-Peierls transition temperature and to the formation of
an antiferromagnetic phase which is expected to appear in disordered
spin-Peierls systems.
 
PACS numbers: 75.30.Kz, 75.50.Ee, 76.30.Da




 
THE DYNAMICS OF THE SORET EFFECT IN THIN FILM OF MAGNETIC FLUID

P. Kopcanskya, L. Tomcoa, M. Timkoa, 
V. Ocelika, M.
Konerackįa, I. Turek b, J. Stelinab 
and C. Musilb
a Institute of Experimental Physics, 
Slovak Academy of Sciences Watsonova
47, 043 53 Kosice, Slovak Republic 

b Department of Technical Physics,
University of Zilina Velky diel, 010 26 Zilina, Slovak Republic

The Soret effect in interference field of two intensive laser beams in
the thin film of magnetic fluid was used to create a periodical structure of
density of magnetic particles. The structures obtained were indicated using
the self-diffraction of the optical beam creating the structures. The
relaxation phenomena after switching off the laser interference field were
discussed in terms of the spectrum of relaxation times. This spectrum is
proportional to hydrodynamic particle size distribution. The relaxation of
optical grating consists of two well-defined channels, i.e. decay through
single particles and small aggregates, respectively.
 
PACS numbers: 66.10.Cb, 75.50.Mm



 
MAGNETIC TRANSITION IN La1/3Nd1/3Ca1/3MnO3 
PEROVSKITE INDUCED BY ELECTRIC FIELD AT A GIVEN MAGNETIC FIELD

J. Baszyńskia, A. Kowalczyka 
and J. Kovįcb
a Institute of Molecular Physics, 
Polish Academy of Sciences,
Smoluchowskiego 17, 60-179 Poznań, Poland 

b Institute of Experimental Physics, Watsonova
47, 043-53 Kosice, Slovakia

We report the discovery of new effect in 
La1/3Nd1/3Ca1/3MnO3 
- the jump of magnetization induced by external electric field E
(2.5-4)V/cm at a given magnetic field H (18-25) kOe at T=4.2 K. This
effect is large when compared with a metamagnetic transition induced by the
magnetic field in many substances. The origin of the magnetization jump
induced by external electric field has not yet been explained. We assume
that this transition is induced by the hopping of E-excited eg 
electrons and
that this is a source of a jumpwise increase in magnetization in the
non-collinear magnetic phase within the perovskite. This effect can be
attributed to a strong coupling between carriers induced by the electric
field (the conduction electrons eg), and the local magnetic moments
(t2g-localized spins) through a mechanism of the Zener double
exchange.
 
PACS numbers: 75.30.Et



 
HEAT CAPACITY AND ELASTIC CONSTANTS OF Fe3-xZnxO4 IN THE VICINITY
OF THE VERWEY TRANSITION

A. Kozlowskia, Z. Kakola, H. Schwenkb, S. Bareiterb, C.
Hinkelb,
B. Luthib and J.M. Honigc
a Dept. of Solid State Physics, 
Faculty of Physics and Nuclear Techniques
University of Mining and Metallurgy Mickiewicza 30, 30-059 Kraków, Poland

b Physikalisches Institut der Universität Frankfurt am Main, Germany

c Dept. of Chemistry, Purdue University, West Lafayette, IN, USA

The results of the heat capacity and elastic constant studies of
Fe3-xZnxO4 (x<0.04) series are reported. Adiabatic heat
capacity measurements, performed on single crystals, show the clear change
of
the transition character from first order for low Zn content (x<0.012) to
the
higher order in 0.012<x<0.035 regime. The change of transition order is
accompanied by the change in the heat capacity base lines below the Verwey
transition temperature TV. From the elastic constants measurements we
found that c11, (c11-c12) and c44 modes exhibit anomalies at
TV but only shear wave c44 show critical softening while approaching
transition from high temperatures. This behavior can be linked to the
results
obtained by the heat capacity studies. These point to the important role of
the lattice contribution to the mechanism of the Verwey 
transition.
 
PACS numbers: 62.20.Dc, 63.20.-e, 64.60.-i, 65.40.+g



 

MAGNETOELASTIC AND OPTICAL STUDIES OF LOW TEMPERATURE MAGNETIC
RELAXATION IN RARE-EARTH ORTHOALUMINATES WITH ISING IONS

I. Krynetskiia, A. Popkovb, M.T. Borowiecc, 
H. Szymczakc and T.
Zayarnyukc
a Moscow State University, 
119899, Vorob'evu Goru, Moscow, Russia 

b State
Research Institute for Physical Problems 103460, Zelenograd, Moscow, Russia

c Institute of Physics, Polish Academy of Sciences Al. Lotników 32/46,
02-668 Warsaw, Poland

The new class of magnetic materials with low temperature magnetic
relaxation was studied. It was evidenced that the crystal DyAlO3 Nowy  with
antiferromagnetically ordered high anisotropy rare-earth ions showed an
exponential magnetic relaxation. For the first time low temperature magnetic
relaxation was investigated by means of magnetostriction and rare-earth
optical absorption spectra instead of standard magnetization measurements.
The possible mesoscopic nature of tunneling process was suggested.
 
PACS numbers: 75.40.Gb, 75.50.Ee



 

METASTABLE MAGNETIC STRUCTURES IN THE BLUME-CAPEL MODEL

K. Kulakowski a, M. Antoniuka, A. Del Moralb 
and P. Gawrońskia
a Faculty of Physics and Nuclear Techniques, 
University of Mining and
Metallurgy Al. Mickiewicza 30, 30-059 Cracow, Poland 

b Laboratorio de
Magnetismo de Solidos Departamento de Fisica de Materia Condensada,
Universidad de Zaragoza 50009 Zaragoza, Spain

We discuss a first-order phase transition from non-magnetic to
magnetic
phase at T=0. New results are presented on a spontaneously formed magnetic
phase and its energy in the C15 atomic structure, in the presence of the
antiferromagnetic interaction. A dynamic phase diagram is constructed for
the
phase transition. The results are discussed in the context of the
pressure-driven phase transition, which was observed experimentally in
YMn2.
 
PACS numbers: 05.70.Fh, 75.10.Hk, 75.30.Kz



 
EFFECT OF NEUTRON IRRADIATION ON THE EPR SPECTRA OF CuGeO 3

E. Mosiniewicz-Szablewskaa, L. Gladczuka, 
H.A. Dabkowskab, B. Pytelc and 
H. Szymczaka
a Institute of Physics, Polish Academy of Sciences, 
Al. Lotników 32/46, 02-668 Warsaw, Poland 

b Brockhouse Institute for Materials Research,
McMaster University, Hamilton, Canada 

c Institute of Atomic Energy, Otwock-Swierk,
Poland

The influence of neutron irradiation on the electron paramagnetic
resonance spectra of the spin-Peierls compound CuGeO3 was investigated in
the wide temperature range 2-300 K. It was found that the irradiation
induced appreciable changes in the EPR signal intensity, resonance line
width
and g-factor of this material. It was also shown that the irradiation leads
to a decrease in the spin-Peierls transition temperature. For higher
irradiation doses, an antiferromagnetically ordered phase can be observed at
lower temperatures. This phase coexists with the spin-Peierls phase. The
observed decrease in the spin-Peierls transition temperature after
irradiation may be associated with some changes in topological and chemical
short-range order or with the transmutation of the fraction of 63Cu in
the 63Cu(n,alpha)60Co reaction.
 
PACS numbers: 75.30.Kz, 75.50.Ee, 76.30.Da




 
THE NUMERICALLY GENERATED SERIES EXPANSIONS FOR SPIN-LATTICE SYSTEMS

G. Musial
Computational Physics Division, Institute of Physics, A. Mickiewicz
University Umultowska 85, 61-614 Poznań, Poland

The numerically generated series expansions complementary to widely
used computer simulations of the Monte Carlo type, are presented. The
effective algorithm for generation of graphs, which constitute the basis of
series expansions for spin-lattice systems, is introduced. The use of the
numerically generated series expansions to calculate the free energy for the
eight-vertex model is explained and discussed in 
detail.
 
PACS numbers: 02.60.-x, 75.10.Hk, 75.40.Cx



 
DIFFUSIVE REGIME FOR CRITICAL SOUND ATTENUATION AND DISPERSION IN
MAGNETS

A. Pawlak and M. Blaszak
Institute of Physics, A. Mickiewicz 
University Umultowska 85, 61-614 Poznań, Poland

We consider a new regime of sound propagation in magnetic systems
above
the critical point. On the basis of a general statistical model including a
flow of energy between spin and lattice subsystems we found that there is a
region of parameters where the sound attenuation and dispersion can be
expressed in a similar way as for noncritical systems for which only the
heat
conduction matters. Contrary to the case of the classical heat diffusion in
the critical magnetic system both the specific heat, entering the reduced
frequency, as well as the effective amplitude are frequency and temperature
dependent reflecting the critical singularities present in the system near
its critical point.
 
PACS numbers: 05.70.Jk, 62.65.+k



 
CRITICAL SOUND PROPAGATION IN MAGNETIC METALS AND BOTTLENECK PHENOMENA

A. Pawlak
Institute of Physics, A. Mickiewicz University Umultowska 85, 61-614
Poznań, Poland

A semiphenomenological model of sound propagation in a critical
magnetic system is proposed, which takes into account a relaxation of energy
between the system of localised spins and the conduction electron spins as
well as the coupling of the longitudinal phonon to bilinear combination of
spin fluctuations and to the energy densities. A general expression for the
acoustic self-energy is obtained within the one-loop approximation. The
effect of ``bottlenecking'' and its influence on the critical singularities
in the sound characteristics is discussed.
 
PACS numbers: 05.70.Jk, 62.65.+k



 
MONTE CARLO STUDY OF SELECTIVE MAGNETIC DILUTION IN SPINEL STRUCTURE

L. Pytlik
Faculty of Physics and Nuclear Techniques, Academy of Mining and Metallurgy
Al. Mickiewicza 30, 30-059 Kraków, Poland

In the present work results of a Monte Carlo study of magnetic
ordering
and percolation tresholds in selectively diluted spinel structure are
discussed. Classical spin model with the Heisenberg type interactions was
used with additional cubic anisotropy terms. Three types of selective
dilution were studied: separate dilutions of A and B sublattices and a
homogeneous dilution of both sublattices. The results are compared for
various degrees of magnetic competition between first and second neighbours
interactions.
 
PACS numbers: 75.10.Hk, 75.10.Nr, 75.40.Mg, 75.50.Lk, 75.50.Gg



 
A.C. SUSCEPTIBILITY MEASUREMENTS UNDER HIGH PRESSURE UP TO 2.0 GPa

B. Sredniawaa, R. Duraja, R. Zacha 
and M. Guillotb
a Institute of Physics, 
Technical University of Cracow Podchorazych 1,
30-084 Cracow, Poland 

b Laboratoire des Champs Magnétiques Intenses,
CNRS/MPI, BP 166X, 38042 Grenoble Cedex 9, France

A newly developed pressure setup for a.c. susceptibility measurements
in the pressure range up to 2.0 GPa is presented; the temperature domain
extends from 77 to 450 K. The steel pressure chamber contains the sample
located at the center of a set of three compensated pick-up coils and the
pressure and temperature sensors. Either alcohol or extraction naphtha is
used as the liquid pressure transmitting medium. The (P,T) magnetic phase
diagram of (Fe0.975Ni0.025)2P system in 
the pressure range up to 2.0 GPa is reported.
 
PACS numbers: 75.50.Cc, 07.55.Jg, 71.20.Lp



 

MAGNETOELASTIC PHASE TRANSITIONS AND CRITICAL BEHAVIOUR OF
(Fe1-xNix)2P SYSTEM

B. Sredniawaa, R. Duraja, A. Pacynab, 
A. Bombikc, R. Zacha, M.
Bacmannd, D. Fruchartd, S. Niziolc, 
P. Fornala and J. Staneke
a Institute of Physics, 
Technical University of Cracow Podchorazych 1,
30-084 Cracow, Poland 

b IFJ, Radzikowskiego 152, 31-342 Cracow, Poland

c WFiTJ, AGH, Al. Mickiewicza 30, 30-059 Cracow, Poland 

d Lab.
Cristallographie, CNRS, BP 166X, Av. Martyrs, Grenoble, France 

e IF UJ, Reymonta 4, 30-059 Cracow, Poland

This report focuses on magnetoelastic properties and critical
behaviour of (Fe1-xNix)2P system. 
For low Ni content (x=0.01) an isolated
critical point was found. Analysis of this critical behaviour in the frame
of molecular field approximation was carried out. Moreover, thermal variations
of the lattice parameters, as measured by X-ray diffraction techniques, were
studied. The (P,T) phase diagrams obtained for several Ni contents show the
evidence that the Curie temperature decreases with pressure. The Mössbauer
spectra collected for x = 0.025, 0.1, 0.2, 0.25 at different temperatures are
also analysed. The existence of two nonequivalent crystallographic sites
occupied by iron atoms as well as local magnetic structure 
is discussed.
 
PACS numbers: 75.50.Cc, 71.20.Lp



 
SU(2) COHERENT STATE PATH INTEGRAL INVESTIGATION OF THE HOLSTEIN DIMER

T. Hakioglua, V.A. Ivanovb 
and M.Ye. Zhuravlevb
a Bilkent University, 
Department of Physics, 06533 Ankara, Turkey 

b N.S. Kurnakov Institute of General and Inorganic Chemistry of the RAS 117907
Moscow, Russia

The SU(2) coherent state path integral is used to investigate the
partition function of the Holstein dimer. This approach naturally takes into
account the dynamical symmetry of the model. The ground-state energy and the
number of the phonons are calculated as functions of the parameters of the
Hamiltonian. The renormalizations of the phonon frequency and electron
hopping for bonding and antibonding states are considered. The destruction
of quasiclassical mean field solution is 
discussed.
 
PACS numbers: 03.65.Db, 71.36.+c, 64.60.Ak




 
SPIN-1/2 PERIODIC NONUNIFORM XX CHAINS AND THE SPIN-PEIERLS
INSTABILITY

O. Derzhkoa,b, J. Richterc 
and O. Zaburannyib
a Institute for Condensed Matter 
Physics, 1 Svientsitskii St., L'viv-11, 290011, Ukraine 

b Chair of Theoretical Physics, Ivan Franko State
University
of L'viv 12 Drahomanov St., L'viv-5, 290005, Ukraine 

c Institut für
Theoretische Physik, Universität Magdeburg P.O. Box 4120, 39016 Magdeburg,
Germany

Using continued fractions we obtained the exact result for the density
of magnon states of the regularly alternating spin-1/2 XX chain with the
Dzyaloshinskii-Moriya interaction. We examined the stability of the
magnetic chain with respect to the spin-Peierls 
dimerization.
 
PACS numbers: 75.10.-b



 
EQUATIONS OF MOTION FOR A CHARGED PARTICLE IN n-DIMENSIONAL MAGNETIC
FIELD

W. Florek and M. Thomas
Institute of Physics, Adam Mickiewicz 
University Umultowska 85, 61-614 Poznań, Poland

The equation of motion for a charged particle moving in the
n-dimensional constant magnetic field is obtained for any linear gauge and
any metric tensor by generalization of Johnson and Lipmann's approach. It
allows to consider the magnetic orbits in the n-dimensional space. It is
shown that the movement of a particle can always be decomposed into a number
of two-dimensional cyclotronic motions and a free particle 
part.
 
PACS numbers: 02.20.-a, 03.65.Bz



 
THE MAGNETIC SPECIFIC HEAT OF THE BEG MODEL

M. Gzik-Szumiata and T. Balcerzak
Department of Solid State Physics, 
University of Lódz Pomorska 149/153,
90-236 Lódz, Poland

The magnetic contribution to the specific heat of the
Blume-Emery-Griffiths model with spin-one is studied by the
cluster variational method in pair approximation. The nearest neighbour
correlation functions are taken into account. The temperature dependencies
of
the specific heat are calculated and discussed in the context of the phase
diagrams obtained recently for the thin film with bilayer 
geometry.
 
PACS numbers: 75.10.-b, 75.70.-i



 
SIMULATED ANNEALING WITH TSALLIS WEIGHTS FOR ± J SPIN GLASS

J. Klosa,b and S. Kobeb
a Institut 
für Theoretische Physik, Technische Universität Dresden
01062 Dresden, Germany 

b Instytut Fizyki, Uniwersytet im. A. Mickiewicza,
Coll. Physicum Umultowska 85, 61-614 Poznań, Poland

Recently, on the basis of the Tsallis distribution of states the
generalized Monte Carlo acceptance probabilities have been proposed and
applied to various optimization problems. In the paper we used the
generalized simulated annealing algorithms for the ± J spin glass model.
Efficiency of the new annealing procedures was compared with that of the
conventional methods. This was done with respect to the number of annealing
steps and to the lowest energy found. The algorithms were applied to a
system
of 70×70 spins on a square lattice with periodical boundary conditions
whose ground state configurations are known exactly. This enables us to
evaluate the efficiency in a quantitative way.
 
PACS numbers: 05.50.+q, 64.60.Cn, 75.10.Hk



 
SYNCHRONIZATION AMONG SPIN-WAVE AMPLITUDES IN CHAOTIC NONLINEAR
FERROMAGNETIC RESONANCE

A. Krawiecki
Institute of Physics, Warsaw University of Technology 
Koszykowa 75, 00-662 Warsaw, Poland

A model of chaos in high-power ferromagnetic resonance in coincidence
regime, based on three-magnon interactions of the uniform mode with a group
of pairs of parametric spin waves, is investigated numerically. The results
are interpreted from the point of view of chaotic synchronization theory. If
all spin waves are identical, all of them are excited above the first-order
Suhl instability threshold and in the chaotic regime their amplitudes show
marginal synchronization, i.e. they differ only by a multiplicative factor,
constant in time. If spin waves have slightly different instability
thresholds, only one or few of them are excited. In the latter case,
addition
of weak thermal noise changes the results qualitatively. For low rf field
amplitude, but above the threshold for chaos, still only few spin-wave pairs
are excited above the thermal level. For higher rf field amplitude all spin
waves in the group are excited, and their amplitudes are not synchronized.
These results suggest that low correlation dimension of chaotic attractors,
observed often in nonlinear ferromagnetic resonance, can be connected with
chaotic synchronization among spin-wave amplitudes, in particular just above
the threshold for chaos.
 
PACS numbers: 76.50.+g, 75.30.Ds, 05.45.+b




 

DIAGONALIZATION OF A BOSONIC QUADRATIC FORM USING CCM: APPLICATION ON A
SYSTEM WITH TWO INTERPENETRATING SQUARE LATTICE ANTIFERROMAGNETS

S.E. Krüger, D. Schmalfuss and J. Richter
Institut 
für Theoretische Physik, Universität Magdeburg PF 4120, 39016
Magdeburg, Germany

While the diagonalization of a quadratic bosonic form can always be
done using a Bogolyubov transformation, the practical implementation for
systems with a large number of different bosons is a tedious analytical
task.
Here we use the coupled cluster method to exactly diagonalise such
complicated quadratic forms. This yields to a straightforward algorithm
which
can easily be implemented using computer algebra even for a large number of
different bosons. We apply this method on a Heisenberg system with two
interpenetrating square lattice antiferromagnets, which is a model for the
quasi-2D antiferromagnet Ba2Cu3O4Cl2. 
Using a four-magnon spin wave
approximation we get a complicated Hamiltonian with four different bosons,
which is treated with coupled cluster method. Results are presented for
magnetic ground state 
correlations.
 
PACS numbers: 75.50.Ee, 75.30.Ds, 31.15.Dv, 42.50.Lc



 
THE INFLUENCE OF NON-MAGNETIC SUBSTRATE ON SPATIAL DISTRIBUTION OF
GAUSSIAN FLUCTUATIONS OF MOLECULAR FIELD IN MAGNETIC NANOPARTICLES AND
ULTRATHIN FILMS

R. Losiński and Z. Onyszkiewicz
Institute of Physics, 
A. Mickiewicz University Umultowska 85, 61-614
Poznań, Poland

An Ising (s=1) model of ferromagnetic nanoparticles and ultrathin
films of the sc structure deposited on a non-magnetic substrate is considered. The
substrate was assumed to affect the crystal field around the atoms lying
closest to it. Consequently, the one-ion anisotropy constant of spin moments
of these atoms becomes dependent on the appropriate component of the tensor
of the magnetic structure deformation. This dependence was assumed to be
linear. To obtain approximations of the Gaussian fluctuations of molecular
field, the generalised equilibrium reduced density operator, along with the
Feynman diagram technique were used. As a result, temperature dependences of
the spatial distributions of mean fluctuations of the magnetic field versus
the changes in the one-ion anisotropy constant induced by the non-magnetic
substrate were obtained.
 
PACS numbers: 75.10.Hk, 75.70.-i



 
TRANSFER-MATRIX SIMULATIONS OF LINEAR MAGNETIC SYSTEMS

R. Matysiaka, A. Caramico D'Auriab, 
F. Espositob and U. Espositob
a Computational 
Physics Division, Institute of Physics, A. Mickiewicz
University Umultowska 85, 61-614 Poznań, Poland 

b Dipartimento di Scienze
Fisiche, Universitį di Napoli Piazzale Tecchio, 80125 Napoli, and INFM
Unitį di Napoli, Italy

The quantum transfer-matrix method was applied to study the
finite-temperature static properties of the spin S=1 antiferromagnetic
Heisenberg chains in a wide range of the single-ion anisotropy and
temperatures. The high-resolution quantum transfer-matrix simulation data
are
obtained for the zero-field susceptibility, specific heat as well as for the
field-dependent magnetization. The microscopic parameters of a number of
real quasi-one-dimensional compounds are found from fitting procedures, some
theoretical approaches are numerically verified and an extension of the
technique to a non-uniform bond alternating molecular magnets is also put
forward.
 
PACS numbers: 75.10.Jm, 75.40.Cx, 75.40.Mg



 
IMPORTANCE OF THE SPIN--ORBIT COUPLING FOR 3d-ION COMPOUNDS: THE CASE OF NiO

R.J. Radwańskia,b 
and Z. Ropkaa
a Center for Solid State Physics, 
sw. Filip 5, 31-150 Kraków, Poland

b Institute of Physics, Pedagogical University Podchorazych 2, 30-084
Kraków, Poland

The orbital and spin moment of the Ni2+ ion in NiO has been
calculated at 0 K to be 0.5 4 µB and 1.99 µB 
respectively. Such
large orbital moment, more than 20% of the total moment of 2.53 
µB,
proves the need for the ``unquenching'' of the orbital moment in compounds
containing 3d ions. It turns out that the spin-orbit coupling is
indispensable for description of magnetic and electronic properties of
3d-ion compounds.
 
PACS numbers: 75.20.Hr, 71.70.Ej



 
EXCHANGE STIFFNESS PARAMETER AND MAGNETIZATION IN PSEUDOPOTENTIAL
CALCULATIONS

W. Schmidt
Institute of Molecular Physics, Polish Academy 
of Sciences Smoluchowskiego
17, 60-179 Poznań, Poland

We study low temperature magnetic properties of transition metals. The
ground state spontaneous magnetization is calculated in a pseudopotential
approximation. In the calculations, the core electronic orbitals are
approximated by asymptotic expressions. The magnetizations are calculated
for
uniform spin densities of valence (chemically active) electrons and in the
Lindhard approximation. Our calculations of the Bloch wall parameter and the
magnon stiffness constant are based on a study of ferromagnetic and
paramagnetic phases. A simple Bragg-Williams approximation between energy
of spin polarization and the time-average of the spin moment per atom
determines the ``exchange coupling'' (Heisenberg-like) for spin-polarized
nearest neighbour Wigner-Seitz cells. Ab initio numerical results of
the spontaneous magnetization, the Bloch wall parameter, and the magnon
stiffness constant are obtained 
for Fe, Co, and Ni.
 
PACS numbers: 71.15.Mb, 71.15.Hx, 75.30.Et



 
HEISENBERG ANTIFERROMAGNET ON A 1/7-DEPLETED TRIANGULAR LATTICE

J. Schulenburga, J. Richtera and 
D.D. Bettsb
a Institut für Theoretische Physik, 
Uni Magdeburg, Germany 

b Department of
Physics, Dalhousie University, Halifax, NS, B3H 3J5, Canada

Based on the triangular lattice and its depletions there are three
simple frustrated antiferromagnetic Heisenberg models in two dimensions. The
first two, the triangular and kagomé lattices, have been examined in the
recent past. The triangular lattice seems to have a long range order whereas
the kagomé does not show the long range order. But these results are still
controversial. This work is concentrated on a third type of this lattice
family in order to improve the understanding of the connection between the
long range order and coordination number in low dimensional systems. Bets
has
described the geometric properties of this lattice. It has a coordination
number 5, which lies precisely between coordination numbers 6 and 4 of the
other two lattices. The low-lying spectra and the correlation functions of
finite lattices have been examined to discuss the possibility of a long
range
ordered ground state in the 1/7-depleted triangular lattice. The low-lying
spectrum is generated by an exact diagonalization, and the tower of
states behavior points to a long range ordered ground 
state.
 
PACS numbers: 75.10.Hk, 75.10.Jm, 75.40.Mg, 75.50.Ee



 
SIMULATIONS OF NOISE-FREE STOCHASTIC RESONANCE IN SPIN-WAVE CHAOS

A. Krawieckia, E. Reiboldd, H. Bennerd 
and A. Sukiennickia,b,c
a Institute of Physics, 
Warsaw University of Technology Koszykowa 75, 00-662 Warsaw, Poland 

b Department of Solid State Physics, University of Lódz
Pomorska 149/153, 90-283 Lódz, Poland 

c Institute of Physics, Polish
Academy of Sciences Al. Lotników 32/46, 02-668 Warsaw, Poland 

d Institut 
für Festkörperphysik, Technische Universität Darmstadt
Hochschulstraße 6, 64289 Darmstadt, Germany

Numerical simulations of noise-free stochastic resonance and aperiodic
stochastic resonance in chaotic ferromagnetic resonance are presented. The
model, based on three-magnon interactions between the externally excited
uniform mode and pairs of spin waves, shows on-off intermittency. The rf
magnetic field amplitude is slowly modulated by a small periodic or
aperiodic 
signal, and the output signal, which reflects the occurrence of laminar
phases and bursts in the time series of spin-wave amplitudes, is analyzed.
On 
variation of the dc magnetic field the signal-to-noise ratio of the output
signal and the correlation function between modulation and output signal
pass
a maximum, which indicates the occurrence of periodic and aperiodic
stochastic resonance, respectively. The role of thermal magnon excitations
in
the occurrence of this maximum is clarified. The results are compared with
experimental findings obtained in other types of 
intermittency.
 
PACS numbers: 76.50.+g, 75.30.Ds, 05.45.+b, 05.40.+j



 
MARSHALL-PEIERLS SIGN RULE IN FRUSTRATED HEISENBERG CHAINS

A. Voigt and J. Richter
Institut für Theoretische Physik, 
Otto-von-Guericke-UniversitØat
Magdeburg Postfach 4120, 39106 Magdeburg, Germany 

We consider the frustrated antiferromagnetic s=1 Heisenberg quantum
spin chain with regard to the Marshall-Peierls sign rule. Using exact
diagonalization data we investigate the breakdown of the Marshall- Peierls
sign rule in dependence on frustration and compare our findings with data
for s=1/2. We calculate a critical value of frustration 
J2crit, where the
Marshall-Peierls sign rule is violated. The extrapolation of this value to
the infinite chain limit holds J2crit approx 0.016, 
lower than in the
case of s=1/2 (J2crit approx 0.027). T
his points to a stronger
influence of frustration in the case of s=1. Nevertheless, the calculation
of
the weight of the Ising-states violating the Marshall- Peierls sign rule
shows that the latter holds approximately even for a quite large frustration
and may be used for numerical techniques.
 
PACS numbers: 75.10.Jm, 75.40.Mg, 75.50.Ee



 
A NEURAL NETWORK MODEL OF AN ISING SPIN GLASS

K.F. Wilson and D.J. Goossens
Department of Physics, Monash University, 
Clayton 3168, Australia

The behaviour of an Ising spin glass (S=1/2) with infinite range
interactions is modelled using a numerical simulation based on a neural
network. Thermodynamic variables are defined on the network, and are found
to
obey the Thouless-Anderson-Palmer theory when the applied magnetic field
is
zero. When a magnetic field is applied along the spin direction, complex
field-dependent behaviour appears, including a state in which the
Edwards-Anderson order parameter is independent of temperature below the
critical temperature.
 
PACS numbers: 75.10.-b, 75.10.Nr, 84.35.+i





 






  IF PAN Home Page
           
  ACTA Home Page