CHEMICAL POTENTIAL AS A DETECTOR OF PHASE TRANSITIONS IN SOLIDS
M. Matlaka, E. Goslawskaa,
B. Grabieca and Kh. Eidb
a Institute of Physics, Silesian University, Uniwersytecka 4, 40-007
Katowice, Poland
b Physics Department, Faculty of Education, Ain-Shams
University, Roxy, Cairo, Egypt
We show that the chemical potential exhibits small but distinct
kinks
at all critical temperatures as the evidence for phase transitions in
the
electronic system, structural phase transitions included. In the case
of, at
least, two kinds of interacting electrons average occupation numbers
exhibit
the same behavior.
PACS numbers: 74.70.-b, 75.30.Kz, 75.40.Cx
|
SUPERCONDUCTING AND MAGNETIC PHASES WITH 1212-TYPE OF STRUCTURE
E.P. Khlybova,b, I.E. Kostylevab,
K. Nenkova ,c, V.I.
Nizhankovskiia, T. Palewskia
and J. Warchulskaa
a International Laboratory of High Magnetic Fields and Low
Temperatures
Gajowicka 95, 53-421, Wroclaw, Poland
b Institute of High Pressure
Physics, 142092 Troitsk Moscow reg, Russia
c Institut fur Festkörper- und
Werkstofforschung Dresden P.O.Box 270016, 01171 Dresden, Germany
Studies of magnetic and transport properties of the 1212 compounds
MA'2A''Cu2O7-x (M 3D Al or Tl; A'= Sr
or Ba; A''= RE, Y, and Ca) revealed a
number of interesting magnetic phenomena. Apart from high-temperature
superconductivity, these compounds exhibit spontaneous
antiferromagnetism,
field induced antiferromagnetism or ferromagnetism. The different
magnetic
orders and superconductivity may be realized in the same compound as a
result of the phase separation.
PACS numbers: 74.25.Ha, 74.72.Jt
|
COMPARISON OF FLUX PINNING IN SINGLE CRYSTALS AND MELT-TEXTURED
YBa2Cu3O7-x
R. Puzniak1, A. Wisniewski1, M. Baran1
and L. Zhou2
1 Institute
of Physics, Polish Academy of Sciences Al. Lotników 32/46, 02-668
Warsaw,
Poland 2Northwest Institute for Nonferrous Metal Research, Xi'an, P.R.
China
Flux pinning properties of single crystals and melt-textured
samples of
YBa2Cu3O7-x were studied for external magnetic
field oriented parallel
and perpendicular to the CuO2 planes (ab-planes). For H || ab
vortex
behaviour is mainly determined by a very effective intrinsic pinning
mechanism. The irreversibility line is located in the region of higher
fields
and temperatures in comparison with the irreversibility line for H perp ab.
In a single crystal for H\perp ab, we observed an increase in the
critical
current density jc with magnetic field - the so-called ``fishtail
effect'' - in a very broad temperature range. For H || ab, this
effect is observed only at temperatures close to Tc, when the intrinsic
pinning is much weaker.
PACS numbers: 74.60.Ge, 74.60.Jg, 74.72.Bk
|
LIEB-MATTIS MODEL FOR TWO INTERPENETRATING ANTIFERROMAGNETS
D. Schmalfuss, S.E. Krüger and J. Richter
Institut für Theoretische Physik, Universität Magdeburg PF 4120,
39016 Magdeburg, Germany
We investigate a frustrated Lieb-Mattis-like spin-1/2 model
that is
a reference model for the corresponding square-lattice Heisenberg model
describing the unusual magnetic properties of
Ba2Cu3O4Cl2. Due to
frustration we obtain a rich magnetic phase diagram. We find two
critical
temperatures in accordance with recent experiments on
Ba2Cu3O4Cl2.
PACS numbers: 75.10.Jm
|
CORRELATION INDUCED OPTIMIZATION OF WAVE FUNCTIONS: THE HUBBARD
CHAIN
J. Spalek, R. Podsiadly
Marian Smoluchowski Institute of Physics, Jagiellonian University
Reymonta 4, 30-059 Kraków, Poland
and W. Wójcik
Institute of Physics, Tadeusz Kosciuszko Technical University
Podchorazych 1, 30-084 Kraków, Poland
We determine the explicit form of the single-particle Wannier
functions
{wi(r)} appearing in the parameters of quantum models. The method
is illustrated on the example of the Hubbard chain, for which we derive the
renormalized wave equation starting from a variational principle and by
treating the system ground state energy as a functional of {wi(r)} and
their derivatives. In this manner, the optimized basis is obtained only
after the electronic correlations have been included in the rigorous
Lieb-Wu solution. The results for the ground state energy and the size
of the renormalized s-type orbitals, both as a function of interatomic
distance, are calculated explicitly.
PACS numbers: 71.10.Fd, 71.15.Fv, 31.25.Nj
|
COQBLIN-SCHRIEFFER IMPURITY WITH LOCAL EXCHANGE COUPLING: A
PERTURBATIVE APPROACH
P. Stefański
Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego 17, 60-179 Poznań, Poland
The Coqblin-Schrieffer one-impurity model with the additional
local
exchange interaction is studied within diagrammatic approach. The
Ruderman-Kittel-Kasuya-Yoshida-type local exchange interaction between
f electrons
of the impurity and a channel of conduction electron l=0 partial waves
is
treated in the molecular field approximation. The perturbation expansion
resummation for the Coqblin-Schrieffer hybridization mediated
interaction
vertex part is carried out in the ladder approximation yielding the
formula
for the Kondo temperature TK decreasing with increased local exchange.
Moreover, the temperature divergence of the susceptibility at TK is
shifted towards T=0. For some critical strength of the local exchange
interaction the susceptibility approaches a Curie-type dependence as for
an
uncompensated impurity magnetic moment. A relation to the ``Kondo
disorder''
model, which leads to the non-Fermi-liquid behavior, is discussed.
PACS numbers: 71.10.Hf, 71.20.Eh, 72.15.Qm, 75.20.Hr
|
STUDY OF COMPOSITES CONSISTING OF HIGH-Tc SUPERCONDUCTOR AND FINE
MAGNETIC PARTICLES
M. Timkoa, P. Kopcanskya, J. Kovavca,
M. Konerackaa and V. Plechacekb
a Institute of Experimental Physics, Slovak Academy of Sciences
Watsonova 47, 043 53 Kosice, Slovak Republic
b Institute of Physics, Czech
Academy of Sciences Cukrovarnicka 10, 162 00 Praha 6, Czech Republic
The composite systems as a mixture of fine magnetic particles of
Fe3O4 and superconducting powder such as
Bi1.8Pb0.2Sr2Ca2Cu3O10+x
were prepared. The influence of internal magnetic field
(generated by magnetic particles) on the superconducting properties of
prepared composites were studied as a function of concentration of
magnetic
particles and their magnetic state. The observed data both of the
shielding
and the Meissner effect were compared with corresponding linear
combination
of pure signals of magnetite and superconductor, respectively. The large
differences were observed for demagnetized samples. It means that result
must be discussed in the frame of the distribution of internal magnetic field
created by the magnetic particles.
PACS numbers: 74.72.Hs, 75.50.Tt
|
PHASE FLUCTUATIONS AND BCS-LP CROSSOVER IN 2D SHORT COHERENCE
LENGTH SUPERCONDUCTORS
B. Tobijaszewska and R. Micnas
Institute of Physics, A. Mickiewicz University Umultowska 85, 61-614
Poznań, Poland
We study the effects of phase fluctuations in 2D short-coherence
length
superconductors on the basis of the extended Hubbard model with
intersite
attraction. In the Kosterlitz-Thouless scenario the critical
temperatures
for anisotropic pairings were determined and compared with the ones from
BCS
Hartree-Fock approximation. The Uemura-type plots, i.e. the critical
temperature vs. zero temperature phase stiffness, were obtained for
extended
s-wave and dx2-y2-wave pairings.
We also discuss the crossover from BCS
to local pair superconductivity for d-wave pairing.
PACS numbers: 74.20.-z, 71.10.Fd, 74.20.Fg, 74.20.Mn, 74.72.-h
|
TRANSPORT PROPERTIES OF THE U1-xThxPt SYSTEM
V.H. Tran and R. Troc
W. Trzebiatowski Institute of Low Temperature and Structure Research
Polish Academy of Sciences, P.O. Box 1410, 50-950 Wroclaw, Poland
We present the results of measurements of electrical resistivity
(rho(T)) and magnetoresistance (Delta varrho varrho0(T))
on the solid
solutions U1-xThxPt (x=0-0.8). The Curie temperature (Tc=21 K)
found for the parent compound UPt, is steadily reduced upon the
Th-substitution.
The rho(T) and Delta varrho varrho0(T)
functions provide evidence
of electron scattering due to spin fluctuations. The most interesting
feature of
Delta varrho varrho0
is its high value of about -22% found for UPt and
U0.9Th0.1Pt at their Tc
and B=8 T. For samples with x >= 0.2, the
value of Delta varrho varrho0
at 4 K and 8 T increases with x and
becomes positive for Th-composition x >= 0.6.
PACS numbers: 72.15.Eb, 72.15.Gd, 75.70.Pa
|
DESTRUCTION OF ANTIFERROMAGNETIC ORDER BY LOCALIZED POLARONS
Z. Wilamowski and E.M. Hankiewicz
Institute of Physics, Polish Academy of Sciences Al. Lotników 32/46,
02-668 Warszawa, Poland
Analysis of a finite spin cluster indicates a possibility of the
formation of purely magnetic polarons in low-dimensional
antiferromagnets. It
is shown that for parameters characteristic of CuO2 based
superconductors a
strong antiferromagnetic polaron can occur. The destruction of
antiferromagnetic order by the presence of a magnetic polaron is
discussed.
PACS numbers: 74.20.-z, 75.10.-b, 74.20.Mn
|
THE REMARK ABOUT AN ANALOGY BETWEEN MAGNETOCALORIC BEHAVIOUR OF TYPE
II SUPERCONDUCTORS AND FERROMAGNETIC MATERIALS
Z. Kalva and P. Manek
Center for Theoretical Study, Charles University and the Academy of
Sciences
Jilska 1, 11000 Praha 1, Czech Republic
The analogy between magnetocaloric behaviour of type II
superconductors
and anisotropic ferromagnetic materials is discussed. Special attention
is devoted to the influence of anisotropy on the negative magnetocaloric
effect near phase transitions.
PACS numbers: 75.30.Sg, 74.60.Ge
|
THERMODYNAMICS OF PSEUDOSPIN-ELECTRON MODEL IN THE U=0 LIMIT
I.V. Stasyuk, A.M. Shvaika and K.V. Tabunshchyk
Institute for Condensed Matter Physics, National Academy of Sciences of
Ukraine 1 Svientsitskii Str., 290011 Lviv, Ukraine
Analytical consideration of a pseudospin-electron model in the
absence of electron correlations is presented. Pseudospin and electron number
mean
values, thermodynamic potential, pair correlation functions are obtained
in the same self-consistent approximation. The possibility of either first
or second order phase transitions between different uniform phases
(bistability)
as well as between the uniform and the chessboard one is shown. In the
regime
n={const}, an instability with respect to phase separation can take
place.
PACS numbers: 71.10.Fd, 71.38.+i, 77.80.Bh, 63.20.Ry
|
THEORETICAL STUDY OF PHASE DIAGRAMS FOR REENTRANT SUPERCONDUCTING
Er1-xHoxX, Er1-xGdxX,
Er1-xTmxX, Ho_ xLu1-xX, AND
Sm1-xErxX (X = Rh_4B_4) ALLOYS
E. Gos/lawska and M. Matlak
Institute of Physics, Silesian University, Uniwersytecka 4, 40-007
Katowice, Poland
We consider a simplified version of the s{-}f model, supplemented
by the intersite Cooper pairs interaction between conduction electrons with
opposite spins to investigate ferromagnetic and superconducting
properties of
an alloy Re1-x(1)Rex(2)X
(Re(1),(2) - rare earth
elements, X =
Rh4B4) using the virtual crystal approximation.
For a suitable choice of
the model parameters we can reproduce the phase boundaries of the
experimentally measured phase diagrams for Er1-xHoxX,
Er1-xGdx X,
Er1-xTmxX, HoxLu1-xX,
and Sm1-xErxX alloys.
PACS numbers: 75.30.Kz, 75.40.Cx
|
LOW TEMPERATURE TRANSPORT AND MAGNETIC PROPERTIES OF SmB6
S. Gabania, K. Flachbartb,
V. Pavlikb, E. Konovalovac, Y.
Padernoc and T. Herrmannsdörferd
a Department of Experimental Physics,
P.J. Safarik University Park
Angelinum 9, 04154 Kosice, Slovakia
b Institute of Experimental
Physics, SAS, 04353 Kosice, Slovakia
c Institute for Problems of Materials
Science, UAS, 252680 Kiev, Ukraine ^d Physikalisches Institut,
Universität
Bayreuth, 95440 Bayreuth, Germany
We present results of transport and magnetic properties of three
single-crystalline samples of the intermediate valence small-gap
semiconductor SmB6 at low temperatures. The received resistivity
dependences
of the samples below 0.5 K exhibit an activated behavior with an energy
gap of a few mK. The temperature dependences of the magnetic susceptibility
show an increase below 15 K which can be accounted for by impurities, by bare
Sm3+ ions or by a small amount of in-gap magnetic 4f55d1
states.
PACS numbers: 75.20.Hr, 71.28.+d
|
CURRENT FLUCTUATIONS IN FERROMAGNETIC TUNNEL JUNCTIONS
B.R. Bulkaa, J. Martineka, G. Michaleka
and J. Barnasb
a Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego
17, 60-179 Poznań, Poland ^bDepartment of Physics, A. Mickiewicz
University
Umultowska 85, 61-614 Poznań, Poland
Current shot noise in a double junction consisting of a small
metallic
grain connected to two ferromagnetic electrodes is analysed in the limit
of sequential tunneling. We show that, apart from charge fluctuations,
there are
strong spin fluctuations. We also show that two distinct relaxation
processes
can be distinguished in the frequency dependent current noise: one in a
low
frequency range and corresponding to spin fluctuations and another one in a
high frequency range corresponding to charge fluctuations.
PACS numbers: 75.70.Pa, 73.50.Td, 73.23.Hk, 73.40.Gk
|
CORRELATIONS OF MECHANICAL STRESSES AND MAGNETICAL BEHAVIOUR OF ION
IMPLANTED MAGNETO-OPTICAL LAYERS
F. Hubenthal and K. Röll
University of Kassel, Heinrich-Plett Str. 40, 34132 Kassel, Germany
Magneto-optical materials such as TbFeCo are used for data storage
in a wide range. Especially the perpendicular magnetic anisotropy is
necessary for
high density recording. But the origin of the perpendicular magnetic
anisotropy in these magneto-optical layers is not exactly known. In our
experiments magneto-optical layers were implanted with heavy ions, with the
aim to change the magnetic behaviour of these layers. After the
implantation
there is a dramatical change in the magnetical and mechanical behaviour,
too.
PACS numbers: 61.72.Ww
|
MAGNETIC STRUCTURES IN ULTRATHIN FILMS AND NANOSTRUCTURES:
SIMULATION
J.-C.S. Levya, A. Ghazalib
and E.Yu. Vedmedenkoc
a LPTMC, case 7020, Universite Paris 7, 75251 Paris 5, France
bGPS,
UMR-7588 CNRS, Universites Paris 7 et Paris 6, 75251 Paris 5, France
cMPI
fšr Mikrostrukturphysik, 06120 Halle, Germany
In magnetic ultrathin films and dots, competing exchange,
anisotropy and dipolar couplings lead to a large variety of magnetic structures. These
structures are obtained by means of the Monte Carlo simulations. Three
classes of magnetic structures are obtained according to
anisotropy-to-dipolar energy ratio: Ising striped structures, XY-spin
structures with vortices, and twisted spin phases at the spin =
reorientation
transition. Domain wall nucleation and motion at the coercive field are
also accessible.
PACS numbers: 75.70.Ak, 75.50.Tt, 75.60.Ch, 75.40.Mg
|
MAGNETIC ANISOTROPY IN EuS-PbS MULTILAYERS
T. Storya, C.H.W. Swüsteb,
H.J.M. Swagtenb, W.J.M. de Jongeb,
A. Stachow-Wójcikc,
A. Twardowskic, M. Arciszewskaa, W. Dobrowolskia,
R.R. Galazkaa and A.Yu. Sipatovd
a Institute of Physics, Polish Academy of Sciences Al. Lotników
32/46, 02-668 Warsaw, Poland
b Department of Physics, Eindhoven University of
Technology 5600 MB Eindhoven, The Netherlands
c Institute of
Experimental
Physics, Warsaw University Hoza 69, 00-681 Warsaw, Poland
d Kharkov =
State Polytechnical University, 21, Frunze Street, 310002 Kharkov, Ukraine
We present the results of ferromagnetic resonance studies of the
thickness dependence of magnetic anisotropy in 2 series of EuS-PbS
multilayers grown on (111) BaF2 and (100) KCl substrates with the EuS
thickness varying in the range d=6-70 A. The anisotropy constant K was
found to follow the dependence K(d)=KV+2KS/d , with the surface
term KS
larger for layers grown on BaF2 as compared to KCl. This difference is
discussed in terms of different thermal stress-induced distortions of cubic
crystal lattice of EuS. We found that the thickness of EuS layer
required for
the perpendicular (to the layer) magnetization is d <= 2-3 A, i.e., it
is below 1 monolayer.
PACS numbers: 75.50.Pp, 75.70.Ak
|
MAGNETIC ANISOTROPY IN Co/Nd MULTILAYERS WITH DEPTH-SELECTIVELY
INSERTED
57Fe PROBE LAYER
L.T. Baczewskia, K. Mibub,
T. Nagahamab and T. Shinjob
a Institute of Physics, Polish Academy of Sciences Al. Lotników
32/46, 02-668 Warsaw, Poland
b Institute for Chemical Research, Kyoto
University, Uji, Kyoto-fu, Japan
Multilayers of Co/Nd with probe layer of 2 AA of 57Fe
evaporated in UHV conditions were studied by means of vibrating sample magnetometry
and Mössbauer spectroscopy at T = 4.2 K. Isomer shift, hyperfine field
distribution and direction was obtained from the Mössbauer data
computer fitting. Magnetic anisotropy was studied and discussed. The easy
magnetization direction was close to the perpendicular direction for
both samples but the tendency to perpendicular anisotropy was stronger when
the Fe probe layer was placed in the vicinity of Co/Nd interface.
PACS numbers: 75.30.Gw, 75.70.-i, 76.80.+y
|
TUNNELING MAGNETORESISTANCE IN PLANAR FERROMAGNETIC JUNCTIONS
M. Wilczyński and J. Barnas
a Institute of Physics, Warsaw Technical University Koszykowa 75,
00-662 Warszawa, Poland
b Department of Physics, Adam Mickiewicz University
Umultowska 85, 61-614 Poznań, Poland
Bias dependence of the tunnel magnetoresistance in simple planar
ferromagnetic junctions is considered theoretically within the one-band
model. The limit of sequential tunnelling in double junctions with a
non-magnetic central electrode is studied as well. In this case tunnel
magnetoresistance exists only when the spin relaxation time due to spin-flip
scattering processes inside the central electrode is sufficiently long.
PACS numbers: 72.15.Gd, 73.40.Gk, 75.70.-i
|
INFLUENCE OF FILM THICKNESS ON THE MICROSTRUCTURE AND MAGNETIC
PROPERTIES OF FINEMETIC THIN FILMS
R. Dlugosa, P. Sovaka,
J. Balcerskib, J. Füzera
and P. Kollara
a Faculty of Science,
P.J. Safarik University, Park Angelinum 9,
041 54 Kosice, Slovakia
b Department of Solid State Physics, University of
Lódz Pomorska 149/153, 90-236 Lódz, Poland
The aim of this work was to study the influence of film thickness
on the structure and magnetic properties of finemetic thin films after
annealing. Thin films with the various thickness (from 20 nm up to 700 nm)
were prepared by DC sputtering method. The heat treatments of the films
for further structural and magnetic observations were performed at the
temperature range 300-500 oC for 15 min in vacuum furnace.
Structural
observations were carried out by transmission electron microscopy. Coercivity
was determined from hysteresis loops traced with fluxmeter and Kerr
magnetooptical hysteresisgraph. All the experimental results confirm a
different magnetic behaviour of the thin films according to their
thickness.
PACS numbers: 68.55.Jk, 73.50.Jt, 75.70.Ak
|
COMPLEX MAGNETIC STRUCTURE OF STRONGLY COUPLED Fe/Si MULTILAYERS
J. Dubowika, F. Stobieckia,
B. Szymańskia, Yu.V. Kudryavtsevb,
A. Grabiasc and M. Kopcewiczc
a Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego
17, 60-179 Poznań, Poland
b Institute of Metal Physics, National
Academy of
Sciences of Ukraine Kiev-142, Ukraine ^cInstitute of Electronic Materials
Technology, Wólczyńska 133, 01-919 Warsaw, Poland
Fe/Si multilayers with strong bilinear and biquadratic couplings
were investigated. A complex structure revealed by the Mössbauer
spectroscopy
corresponds to multimode ferromagnetic resonance spectra in a non-saturated
state. Simple dispersion relations for antiferromagnetic coupled bilayer
structures are shown to be inapplicable to the Fe/Si multilayers with a
strong biquadratic component to the antiferromagnetic bilinear coupling.
PACS numbers: 75.70.-i, 68.55.-a, 76.50.+g
|
INTERACTION BETWEEN MAGNETIC LAYERS IN STRUCTURES WITH NARROW-GAP
IV-VI SEMICONDUCTORS
V.K. Dugaeva, V.I. Litvinova, W. Dobrowolskib
and T. Storyb
a Chernovtsy Department of the Institute of Materials Science Problems
Ukrainian Academy of Sciences, Vilde 5, 274001 Chernovtsy, Ukraine
b Institute of Physics, Polish Academy of Sciences
Al. Lotników 32/46, 02-668 Warsaw, Poland
The results of calculation of the indirect exchange interaction
between magnetic layers are presented for the case of a structure with
narrow-gap
semiconducting IV-VI quantum well. The main mechanism is a magnetic
polarization of the size-quantized electrons and holes inside the well.
This type of interaction is suggested for the explanation of recent
experiments on
EuS/PbS structures.
PACS numbers: 75.70.Cn, 75.50.Pp, 75.70.Ak
|
ROLE OF THE SURFACE ENERGY FOR THE FORMATION OF THE DOMAIN STRUCTURE
AT MAGNETOELASTIC PHASE TRANSITION
H.V. Gomonaj and V.M. Loktev
National Technical University of Ukraine ``KPI'' 37, Ave. Peremogy,
252056, Kyiv, Ukraine
The formation of the domain structure during magnetic ordering in
the pure antiferromagnet with the rotational (non-180o) domains can be
treated as thermodynamically preferable if the free energy of the sample
is minimized with the account of surface energy. The analogy between the
role of
magnetostatic energy in ferromagnets and surface energy of
antiferromagnet is
traced. The behavior of the domain structure and macroscopic strain
tensor in
the external magnetic field is investigated.
PACS numbers: 75.50.Ee, 75.60.Ch
|
MAGNETIC PROPERTIES OF IRON-BASED AMORPHOUS AND NANOCRYSTALLINE
Fe-Zr-X-B (X: Cu, Al) ALLOY FILMS
I. Gosciańskaa,
T. Tolińskib, H. Ratajczakb,
P. Sovákc,
R. Dlugosc and M. Koncca Institute
of Physics, A. Mickiewicz University, Umultowska 85, 61-614
Poznań, Poland
b Institute of Molecular Physics, Polish Academy of
Sciences Smoluchowskiego 17, 60-179 Poznań, Poland
c Department of Experimental
Physics, P.J. Safarik University, Kosice, Slovakia
Thermal stability and magnetic properties of thin films, of a few
Fe-based amorphous and nanocrystalline alloys, have been studied. The
alloys
belong to the class Fe-M-B, whose representatives are:
Fe87Zr4Cu1B8,
Fe87Zr7B6, and
Fe87Zr7Al1B5 and are of
particular interest because of their wide variety of magnetic
properties. The
films were prepared by flash evaporation onto liquid nitrogen cooled
substrates. Measurements of the Kerr effect, the Hall effect, and
ferromagnetic resonance in the films were carried out as functions of
the annealing temperature. It was found that the changes in the coercive
field Hc, resonance linewidth Delta Hpp,
effective magnetization Meff,
Hall parameters, and resistance were correlated with the
structural changes in the studied films.
PACS numbers: 73.61.Tm, 75.50.Bb
|
PREISACH MAPS OF MULTILAYERED Co/Cu STRUCTURES
M. Gutowski, M.U. Gutowska, K. Piotrowski, L.T. Baczewski and A. Wawro
Institute of Physics, Polish Academy of Sciences Al. Lotników
32/46, 02-668 Warszawa, Poland
Magnetooptical Kerr effect measurements of room temperature
hysteresis
loops were taken using sandwich- and multilayer-type specimens and
He-Ne
laser light. For maximal external field of ~250 Gs the corresponding
Kerr
angle reached 0.04 deg. The samples were obtained in the Institute of
Physics, Polish Academy of Sciences, Warszawa, using MBE method. The
structure of samples may be described by a formula:
substrate-buffer
layer-(xCo/yCu)n -cover layer. Al2O3
(two orientations) and MgO were
used as substrates, the buffer layer was made of W, Cu or Fe, x=15, 20 or
25 A, y=7, 8, 9, 10, 11, 12, 13, 14, and 20 Ć, n=25 and 30.
50 Ć of
gold (Au) served as a cover layer. The genetic algorithm was
subsequently
used as a data processing tool, in order to reconstruct the Preisach map
for
each hysteresis loop. The diagrams clearly indicate changes of magnetic
interactions caused by varying thicknesses of individual magnetic and
non-magnetic layers.
PACS numbers: 75.40.Mg, 75.60.Ej, 75.70.-i, 78.20.Ls, 78.66.-w
|
COERCIVITY OF ULTRATHIN MAGNETIC FILMS WITH PERPENDICULAR ANISOTROPY
V. Zablotskiia, M. Kisielewskib,
O. Tsiganenkoc and J. Ferred
a Physics Department, Donetsk State University, 340055 Donetsk,
Ukraine
b
Institute of Physics, University at Bialystok, Lipowa 41, 15-424
Bialystok, Poland
c Institute of Physics, Academy of Sciences of Czech Republic Na
Slovance 2, 18040 Praha 8, Czech Republic
d Lab. de Phys. des Solides, URA
CNRS 02, Université Paris-Sud, 91405 Orsay, France
The calculation of the temperature dependence of the domain wall
coercivity of ultrathin magnetic films with perpendicular anisotropy is
reported. In this case, the magnetization reversal is supposed to occur
through domain wall motion. The proposed model takes into account thermal
bending fluctuations of the domain wall, which is pinned by crystal
defects
such as grain boundaries. A fitting procedure, applied to recently published
experimental data on the field induced domain wall velocity in Au/Co films,
allows us to find out realistic values of the involved parameters.
PACS numbers: 75.60.-d, 75.60.Ch, 75.70.Ak
|
CREATION AND OBSERVATION OF DOMAIN STRUCTURES WITH A SPECIAL KERR
MICROSCOPE
S. Knappmanna, K. Rölla
and F. Stobieckib
a University Gh Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany
b Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego 17, 60-179 Poznań, Poland
A Kerr microscope is presented, which on the one hand allows us to
make, in a conventional manner, images of domains in thin films with
perpendicular magnetic anisotropy. On the other hand, it is possible to heat
the sample locally by a focussed laser beam and make images simultaneously.
Therefore, it is possible to write domains thermomagnetically and further to
observe temperature dependent magnetic reorientations. For demonstration
domains have been created thermomagnetically in TbFe multilayers.
Writing with low magnetic field leads to domains with a subdomain structure,
as it has been found previously by Lorentz microscopy.
PACS numbers: 75.70.Kw
|
THE DISTRIBUTION OF MAGNETIZATION FOR A STEPPED FERRO-ANTIFERROMAGNET
INTERFACE
O.K. Dudko and A.S. Kovalev
B. Verkin Institute for Low Temperature Physics and Engineering Ukrainian
Academy of Sciences, 47 Lenin Avenue, 310164 Kharkov, Ukraine
Magnetization distribution of a disclination type connected with the
atomic step on the ferro-antiferromagnet boundary is studied. The
results are generalized for the periodic stepped interface.
PACS numbers: 75.30.Kz
|
THE EMERGENCE OF SUBSURFACE SPIN-WAVES IN FCC (110) MAGNETIC FILMS
S. Mamicaa, H. Puszkarskib
and J.C.S. Lévyb
a Surface Physics Division, Faculty of Physics, Adam Mickiewicz
University
Umultowska 85, 61-614 Poznań, Poland
b Laboratoire de Physique
Théorique
de la Mati\egrave;re Condensée Université
Paris 7-Denis Diderot, 2 Place
Jussieu, 75221 Paris Cedex 05, France
We show that the emergence of subsurface branches in the spin-wave
spectra of thin films is due to the deficiency of interactions with
next-nearestneighbours, the position vectors of which are oblique to
the film surface.
PACS numbers: 75.70.-i, 75.40.Gb, 75.30.Ds
|
SPONTANEOUS SURFACE MAGNETISATION OF SINGLE CRYSTAL MnF2 IN THE
ANTIFERROMAGNETIC STATE
V.I. Nizhankovskiia, A.I. Khar'kovskiia
and A.J. Zaleskib
a International Laboratory of High Magnetic Fields and Low
Temperatures Gajowicka 95, 53-421 Wroclaw, Poland
b Institute of Low Temperature and
Structural Research, Polish Academy of Sciences P.O. Box 937, 50-950
Wroclaw, Poland
Spontaneous magnetisation of (100) and (010) surfaces of a MnF2
single crystal in the antiferromagnetic state is discovered. A sign of the surface
magnetisation is determined by a difference in dielectric constants
varepsilon of MnF2 and ambient matter:
magnetisation is directed to the
substance with a smaller varepsilon.
PACS numbers: 75.30.Pd, 75.25.+z, 75.50.Ee
|
MAGNETIC ANISOTROPY OF NiMn/Ni AND NiMn/Cu/Ni THIN FILMS
T. Ogawa and T. Sato
Department of Instrumentation Engineering, Faculty of Science and Technology
Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522,
Japan
The magnetic anisotropy of reentrant spin glass NiMn thin film, in the
vicinity of the ferromagnetic Ni film, is investigated using NiMn/Ni,
Cu/Ni/Cu (t=10 Ć and 500 Ć)/NiMn and NiMn/Ni/Cu
(t=10 div 5000
Ć)/Ni films. The unidirectional anisotropy field of NiMn layer in
NiMn/Ni film is smaller than that of bulk NiMn. In Cu/Ni/Cu
(t=10 Ć and
500 Ć)/NiMn film, the unidirectional anisotropy field is almost
independent of the Cu spacer thickness. These results can be explained in
terms of magnetic coupling between the magnetic layers in addition to
the film structure of NiMn layer.
PACS numbers: 75.30.Gw, 75.50.Lk, 75.70.Ak
|
CORRELATED ROUGHNESS EFFECTS IN THE GIANT MAGNETORESISTANCE OF MAGNETIC
MULTILAYERS
G. Palasantzasa, J. Barnasb
and J.Th.M. De Hossona
a Department of Applied Physics, Materials Science Center and
Netherlands
Institute for Metals Research University of Groningen, Nijenborgh 4, 9747 AG
Groningen, The Netherlands
b Department of Physics, Adam Mickiewicz
University Umultowska 85, 61-614 Poznań, Poland
Interface roughness effects on the giant magnetoresistance in magnetic
multilayers are analysed theoretically for structures with non-conformal
correlated interfaces. The roughness of each interface is described in terms
of the K-correlation model and is characterized by the roughness
exponent
H(0<=H<1), correlation length xi, and rms roughness amplitude
Delta.
Coherent scattering by different interfaces is also taken into account.
PACS numbers: 72.15.Gd, 73.40.Jn
|
EDGE PINNING EFFECTS AND GIANT THERMAL INSTABILITY OF MAGNETIZATION
HYSTERESIS LOOPS IN THIN NANO-SCALE MAGNETS
A.F. Popkova, L.L. Savchenko^b and N.V. Vorotnikovac
a Zelenograd Research Institute of Physical Problems Zelenograd,
103575 Moscow, Russia
b Physical Department, Moscow State University Vorobjevy
Gory, 119899 Moscow, Russia ^cInstitute of Physics and Technology, Russian
Academy
of Science Nakhimovsky avenue 34, 117218 Moscow, Russia
Magnetization reversal modes of super-thin nano-scale particles
with a high magnetization and low anisotropy are analyzed by solving magnetic
moment
motion equations. A new kind of thermal hysteresis instability connected with
the random mutual transformation of the main magnetization modes is
predicted by simulations.
PACS numbers: 75.60.Ej, 67.80.Jd
|
SPIN-WAVE RESONANCE IN THE FeBr2 METAMAGNETIC THIN FILM
W. Rudziński
Faculty of Physics, Adam Mickiewicz University Umultowska 85, 61-614
Poznań, Poland
The spin-wave resonance in the thin FeBr2 field-induced
metamagnet in
the paramagnetic phase with the (001) surfaces and at low temperatures is
examined theoretically. It is found that the absorption spectrum is
strongly
affected by modifications of the surface exchange parameters. Also, the
conditions for the appearance of various surface and bulk spin-wave features
are discussed.
PACS numbers: 75.30.Ds, 75.70.Ak
|
MAGNETISATION OF Co/Ti MULTILAYERS
K. Smardza, L. Smardzb
and A. Jezierskib
a Inst. of Mater. Sci. and Eng., University of Technology Pl. Curie 5,
60-965 Poznań, Poland
b Institute of Molecular Physics, Polish Academy of
Sciences Smoluchowskiego 17, 60-179 Poznań, Poland
We studied experimentally and theoretically the magnetisation of the
Co/Ti multilayers. The results showed that the magnetic moments on Co atoms
located at the Co-Ti interface are strongly reduced. For dTi=0.35
nm the estimated effective non-magnetic Co thickness at the Co-Ti interface
amounts approx 0.08 nm and approx 0.1 nm at 4 K and 295 K,
respectively. We
found a good agreement between experimentally determined and theoretically
calculated magnetisations.
PACS numbers: 75.70.-i, 75.30.Et
|
MAGNETIC PROPERTIES OF NANOCRYSTALLINE Co/Ti AND Co/Zr MULTILAYERS
L. Smardza and K. Smardzb
a Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego
17, 60-179 Poznań, Poland
b Institute of Mater. Sci. and Eng., University of
Technology Pl. Curie 5, 60-965 Poznań, Poland
It is shown that the Co sublayers grow in the soft magnetic
nanocrystalline phase up to a critical thickness dapprox3 and 2.8 nm
for
Co/Ti and Co/Zr MLs, respectively. The rapid decrease in the interlayer
exchange coupling could be explained by its strong damping due to
formation of a non-magnetic quasi-amorphous Co-Ti and Co-Zr alloy layer at the
interfaces. The nanocrystalline 2.2 nm-Co/2 nm-Ti ML shows a weak 90°
coupling near the transition zone from ferromagnetic to zero coupling.
PACS numbers: 75.70.-i, 75.30.Et
|
MAGNETIC AND ELECTRIC TRANSPORT PROPERTIES OF Fe-Hf-O FILMS
PREPARED BY SUPERSONIC PLASMA JET METHOD
V. Soyka, L. Kraus, Z. Frait, M. Sicha and L. Jastrabik
Institute of Physics, ASCR, Na Slovance 2, 18221 Praha 8, Czech
Republic
The influence of deposition conditions on the structure, magnetic
properties, and electrical resistivity of Fe-Hf-O films, prepared by the
supersonic plasma jet deposition technique, was investigated.
Composition of
the films was controlled by the nozzle composition and the working gas.
It varied in the limits: 15-68 at.% of Fe, 0.5-8 at.% of Hf and 29-80 at.%
of O. The films were mainly X-ray amorphous. Some of them showed a weak
and broad peak near the [110] reflection of alpha-Fe indicating the
presence of
Fe-rich clusters in an amorphous matrix. Depending on the deposition
parameters the magnetic properties vary from paramagnetic to
ferromagnetic
ones. The electrical resistivity changes from the metallic to the hopping
type. In some samples a large negative magnetoresistance is observed.
PACS numbers: 75.50.Kj, 75.70.Pa
|
HYPERFINE FIELD IN YIG WITH CHARGED SUBSTITUTION
J. Kohouta, H. Stepánkováa,
J. Englicha, P. Novákb,
M. Kuceraa and K. Nitschb
a Faculty of Mathematics and Physics,
Charles University 180 00 Prague 8, V
Holesovickách 2, Czech Republic ^bInstitute of Physics, Academy of
Sciences Cukrovarnická 10, 16 253 Prague 6, Czech Republic
57Fe NMR spectra were measured on thin films of yttrium iron
garnet with divalent (Ca2+)
and tetravalent (Ge^{4+}) cation substitutions using
the spin echo technique at 4.2 K. A series of
Y3-xCaxFe5-xGexO12
samples with 0 <= x <= 0.0 5 was prepared by an epitaxial growth from
BaO/B2O3/BaF2
flux on gadolinium gallium garnet substrate. Satellite
lines corresponding to the iron ions having the Ge4+
and Ca2+ in their
neighbourhood were identified. The sample with the germanium content of
x(Ge) = 0.004 and (110) substrate orientation was used for a detailed study:
NMR spectra of this sample were measured in an external magnetic field of 0.1 T
applied along several directions in the plane of the film. The
modification
of the isotropic part and the anisotropy tensor of the hyperfine interaction
caused by the Ge4+ substituent were obtained from the experimental
data.
The results were compared with those previously reported for trivalent
substitution (Ga3+).
PACS numbers: 76.60.-k, 75.50.Gg
|
TEMPERATURE DEPENDENCE OF MAGNETISATION REVERSAL AND GMR IN SPIN VALVE
STRUCTURES
F. Stobieckia, T. Stobieckib,
B. Ockerc, W. Maassc, W.
Powroznikb, A. Pajad, C. Loche
and K. Rölle
a Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego
17, 60-179 Poznań, Poland
b Department of Electronics, University of Mining
and Metallurgy, Krak/ow, Poland ^cBalzers Process Systems GmbH, Alzenau,
Germany
d Department of Solid State Physics, Faculty of Physics and
Nuclear
Techniques University of Mining and Metallurgy, Kraków, Poland
e Department of Physics, University of Kassel, Germany
Temperature measurements of magnetisation reversal, resistance and
magnetoresistance of Co/Cu/Co/FeMn spin valve structures deposited in
different conditions were performed. The influence of exchange
anisotropy
energy, interlayer coupling energy, and electron transport properties were
taken into consideration in explaining differences in giant
magnetoresistance effect of investigated samples.
PACS numbers: 75.70.Pa, 68.55.Ln, 68.55.-a
|
THE IMPROVEMENT OF ATOMIC FORCE MICROSCOPE SUITABLE FOR MAGNETIC
DOMAIN STRUCTURE MEASUREMENTS
I. Sveklo, W. Dobrogowski, M. Kisielewski and A. Maziewski
Institute of Physics of Bialystok University, Lipowa 41, 15-424
Bialystok, Poland
Based on commercial Burleigh METRISTM-2000 Atomic Force
Microscope two methods of magnetic force measurements were realised. The
developed system was successfully applied for study of magnetic
structure of
both YIG-garnet and CoNi/Pt magneto-optic multilayers.
PACS numbers: 75.70.-i, 75.30.Pd, 61.16.Ch
|
DIPOLAR CONTRIBUTIONS TO MAGNETOELASTIC ENERGY OF CRYSTAL GRAINS WITH
INTERFACES
T. Szumiataa, R. Zuberekb, H. Szymczakb
and J. Gonzalezc
a Department of Physics, Technical University of Radom Malczewskiego 29,
26-600 Radom, Poland
b Institute of Physics, Polish Academy of Sciences
Al. Lotników 32/46, 02-668 Warsaw, Poland
c Departamento de Fisica de
Materiales, Universidad del Pais Vasco Paseo Manuel de Lardizabal, 3, 20009
San Sebastian, Spain
The magnetic anisotropy and magnetostriction in nanocrystalline grains
in non-magnetic or magnetic matrix (nanoparticles or nanocrystalline
materials) differ from their bulk properties. The interactions between atoms
at the interface play the important role in these magnetic properties.
In this paper the magnetic dipolar contribution to magnetostriction energy has
been calculated for spherical crystal grains (of bcc and fcc symmetry)
with
interface layer of atoms possessing different magnetic moment. Total
magnetoelastic energy of the sphere-interface system is a sum of
magnetoelastic energy of the sphere, energy of the interactions
between the
sphere and the interface and also the energy of the interface. It was shown
that magnetoelastic energy depends on the sphere size and interface
thickness.
PACS numbers: 75.80.+q, 68.90.+g, 78.66.Jg
|
MAGNETIC PROPERTIES AND GMR OF SPUTTERED PERMALLOY/Au MULTILAYERS
B. Szymański and F. Stobiecki
Institute of Molecular Physics, Polish Academy of Sciences Smoluchowskiego
17, 60-179 Poznań, Poland
We report on structural, magnetic, and GMR properties of
permalloy/Au
multilayers where permalloy = Ni83Fe17,
deposited by face-to-face
sputtering onto Si(111) substrate. X-ray diffraction studies confirmed a good
structural quality of our multilayers. The samples were characterised
with vibrating sample magnetometer, longitudinal magnetooptical Kerr effect and
giant magnetoresistance measurements. It was determined that our
multilayers
are magnetically very soft with Hc approx 1 Oe and show uniaxial
anisotropy with HK approx 5 Oe.
For gold sublayer thickness dAu close
to 1.1 nm the antiferromagnetic coupling is present in very narrow Au
thickness range (approx 0.2 nm). Despite a good structural quality of
samples relatively small giant magnetoresistance value (1.2% at room
temperature) was found. It is due to non-perfect aniferromagnetic
coupling caused by pinholes.
PACS numbers: 75.70.-i, 75.70.Pa, 68.55.-a
|
INFLUENCE OF TEMPERATURE AND ANNEALING ON GMR IN SPUTTERED PERMALLOY/Cu
MULTILAYERS
M. Urbaniaka, F. Stobieckia,
T. Lucińskia, M. Kopcewiczb,
A. Grabiasb and J. Aleksiejewa
a Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego 17, 60-179 Poznań, Poland
b Institute of Electronic
Materials Technology Wólczyńska 133, 01-919 Warszawa, Poland
The influence of temperature and annealing on giant
magnetoresistance
of Si(100)/Cu(20 nm)/Py(2 nm)/(Cu(2 nm)/Py(2 nm))100
multilayer (Py = Ni83Fe17)
sputtered at room temperature in double face-to-face
configuration is reported. It was found that giant magnetoresistance value,
Delta RGMR/Rsat
(where Rsat is the resistance in
saturation), monotonically decreases with increasing temperature (4.5% at
173 K to about 1% at 373 K). This results from the decrease in magnetic
change of resistance, Delta RGMR,
and to the lesser extent from an increase in Rsat,
though both of them are caused by the shortening of
electrons mean free path. The observed almost linear decrease in giant
magnetoresistance saturation field with increasing temperature is explained
by temperature changes of magnetization profile. Vibrating sample
magnetometer measurements revealed that the increase in temperature results
in pronounced decrease in remnant to saturation magnetization ratio
(Mr/Ms) suggesting that at low temperatures magnetic
bridges between Py layers play an important role in magnetization process.
It is shown that proper annealing, by an annihilation of bridges and/or lateral
decoupling, leads to an increase in giant magnetoresistance ratio from 3.4% in as
deposited state to 4.7%.
PACS numbers: 75.70.Ak, 75.70.Pa
|
MAGNETIC CHARACTERISTICS OF THE SYSTEM OF EXCHANGE COUPLED LAYERS
A. Urbaniak-Kucharczyk and S. Machowski
Department of Solid State Physics, University of Lódz Pomorska
149/153, 90-236 Lódz, Poland
Using the Green function method it is shown that the deviation of the
Curie temperature from its value calculated for continuous layers is
related
to the absolute value of the interlayer coupling parameter. The
dependence of
spin wave stiffness parameter on the interlayer exchange coupling is also
found.
PACS numbers: 75.70.Ak, 75.30.-m, 75.40.Cx
|
STM IMAGING OF MAGNETIC DOTS WITH FERROMAGNETIC TIP
A. Wawroa,b and A. Kasuyab
a Institute of Physics, Polish Academy of Sciences
Al. Lotników 32/46,
02-668 Warsaw, Poland ^bInstitute for Materials Research, Tohoku
University
2-1-1 Katahira, 980 Sendai, Japan
We report on imaging of isolated, few nanometers in size, magnetic
dots (Co, Ni) by the use of a scanning tunneling microscope equipped with a
ferromagnetic Co tip in the presence of external magnetic field. The
dependence of apparent height of dots as a function of magnetic field
takes a hysteresis-like shape. We discuss possible mechanisms of the scanning
tunneling microscope tip interactions with dots.
PACS numbers: 34.80.Nz, 36.40.Cg, 61.16.Ch
|
STRUCTURAL STUDIES OF Co/Cu AND Co/Ru INTERFACES USING ^{59}Co NMR METHOD
M. Wójcik, E. Jedryka, S. Nadolski
Institute of Physics, Polish Academy of Sciences Al. Lotników 32/46,
02-668 Warszawa, Poland
D. Kubinski, M. Parsons and H. Holloway
Ford Research Laboratory, SRL/MD3028, Dearborn, MI 48121-2053, USA
The structural and magnetic properties of three magnetron
sputtered
multilayers at the 2nd maximum of antiferromagnetic coupling were studied
using 59Co NMR spectroscopy: [Co(20 Ć)/Cu(20 Ć)]20,
[Co(20 Ć )/
Ru(18 Ć)]20 and a heterostructure, in which non-magnetic spacers
alternated between Cu and Ru. Co/Cu interfaces were found to be relatively
sharp, extended over 3 monolayers, while the Co/Ru interfaces extend
over 6
monolayers due to the good miscibility of Co and Ru. The NMR restoring field
in the heterostructure is found to be the average of the restoring
fields in both reference samples.
PACS numbers: 76.60.Lz, 75.70.Pa, 75.70.Cn, 75.20.En
|
PERPENDICULAR AND PARALLEL TRANSPORT, AND INTERLAYER EXCHANGE COUPLING IN
MAGNETIC TRILAYERS WITH EXTRA CAP-LAYERS
\aut {S. Krompiewski and M. Zwierzycki
Institute of Molecular Physics, Polish Academy of Sciences
Smoluchowskiego
17, 60-179 Poznań, Poland
Oscillations of magnetoresistance and interlayer exchange coupling vs.
both non-magnetic spacer and cap-layer thicknesses are studied within
the framework of the s-d model. The studies are carried out by means of the Kubo
formula and a Green function recursion technique. Transport calculations
concern multilayers (sandwiched between two semi-infinite ideal lead wires)
oriented either parallel or perpendicular to the current direction. The
considered structures for the above mentioned two basic geometries, are cubic
grains identical in: (i) size, (ii) number of sublayers, and (iii)
thicknesses of particular sublayers, which makes it possible to compare,
in a direct and reliable way, the corresponding magnetoresistances. The
current-in-plane magnetoresistance is found to be usually lower than the
current-perpendicular-to-plane one, but both of them show oscillatory
behaviours mutually correlated, and related to the Fermi surface callipers.
Moreover, the current-perpendicular-to-plane giant magnetoresistance for
structures in a form of infinite in layer-plane trilayers capped with an
extra bilayer (ferromagnet/paramagnet) is also discussed.
PACS numbers: 75.70.-i, 75.70.Pa, 73.23.Ad
|
INELASTIC NEUTRON SCATTERING IN gamma-Mn(12%Ge) ALLOY ABOVE AND BELOW
THE NÉEL TEMPERATURE
J. Jankowska-Kisielińskaa, K. Mikkea and B.
Hennionb
a Institute of Atomic Energy, Swierk, 05-400 Otwock, Poland
bLaboratoire
Lèon Brillouin, CEN Saclay, France
The magnetic excitations different from spin waves in the
gamma-Mn(12%Ge) antiferromagnet are the subject of the present
investigation. The inelastic neutron scattering was measured at 4
temperatures above TN. The Lorentzian-type formula for the inelastic
neutron scattering cross-section with the spectral width for a hydrodynamic
region was used for data analysis. The obtained values of the
``stiffness constants'' are of the order of 200 meV Ć\ and they depend weakly on
temperature in the range of 1.04-1.25TN. The inelastic neutron
scattering for energy transfers below and close to the value of the gap
energy of the spin wave spectrum was measured at room temperature. The
observed intensities can be treated as a sum of intensities of neutrons
scattered on spin waves around the magnetic Brillouin zone centre and =
those scattered on fluctuations at the zone boundary.
PACS numbers: 75.40.Gb, 75.30.Ds, 75.20.En
|
THE ENERGY SPECTRUM OF SINGLE-HOLE STATES IN TRANSITION METAL OXIDES
A. Lehmann-Szweykowskaa, R.J. Wojciechowskia
and G.A. Gehringb
a Institute of Physics, A. Mickiewicz Univeresity, Umultowska 85,
61-614 Poznań, Poland
b Department of Physics and Astronomy, University of
Sheffield, Sheffield S3 7RH, U.K.
The p-d hybridised single-hole states of the
transition-metal-oxygen
tetrahedron (TMO4) are collectivised due to the direct p-p hopping
between
oxygens of different clusters. The lowest-lying energy band is always narrow
and fully occupied. The first excited band gets occupied as an effect of
valence-uncompensated doping, so it can be almost localised. The possible
hole excitations to the two higher energy bands, which are wider, may imply
the Mott-like hopping form of charge transport in these systems.
PACS numbers: 71.10.Fd, 72.20.-i
|
EFFECTS OF CORE-HOLE SCREENING ON SPIN-POLARISED AUGER SPECTRA FROM
FERROMAGNETIC Ni
T. Wegner, M. Potthoff and W. Nolting
Lehrstuhl ``Festkörpertheorie'', Institut für Physik,
Humboldt-Universität zu Berlin Invalidenstraße 110, 10115 Berlin,
Germany
We calculate the spin- and temperature-dependent local density of
states for ferromagnetic Ni in the presence of a core hole at a
distinguished
site in the lattice. Correlations among the valence electrons and between
valence and core electrons are described within a multi-band Hubbard
model
which is treated by means of second-order perturbation theory around the
Hartree-Fock solution. The core-hole potential causes strong screening
effects in the Ni valence band. The local magnetic moment is found to be
decreased by a factor of 5-6. The consequences for the spin
polarisation of
CVV Auger electrons are discussed.
PACS numbers: 79.20.Fv, 71.20.Be, 75.60.Ej
|
MAGNETIC PROPERTIES OF SPIN-LADDERS
(A2Cu2O3)m (CuO2)n
M. Barana, H. Szymczaka,
R. Szymczaka, S. Dyeyeva, L. Leonyukb
and G.-J. Babonasc
a Institute of Physics, Polish Academy of Sciences Al. Lotników
32/46,
02-668 Warsaw, Poland ^bMoscow State University, 119899 Moscow, Russian
Federation
c Semiconductor Physics Institute, 2600 Vilnius, Lithuania
Magnetization M(T) and M(H) data of single crystals of the
S=1/2
quasi-one-dimensional system
(A2Cu2O3)m(CuO2)n
with various A-site
constituents are compared. The studied orthorhombic, incommensurate
crystals
are characterized by m/n=5/7,7/10, and 9/13. The role of
rare-earth ions located in A-sites is discussed.
PACS numbers: 75.40.Cx, 75.30.Gw, 75.45.+j, 75.90.+w
|
THE MAGNETIC PROPERTIES AND THE BARKHAUSEN NOISE OF THE ANNEALED Fe-V-B
AMORPHOUS ALLOY
L. Cenigaa, L. Novákb
and A. Zentkoa
a Institute of Experimental Physics, Slovak Academy of Sciences
Watsonova
47, 043 53 Ko\v sice, Slovak Republic ^bDepartment of Physics, Technical
University Komenského park 2, 041 20 Kosice, Slovak Republic
As a consequence of the annealing process, the study of structural
changes which can be followed by measuring structure sensitive magnetic
properties as the stress induced anisotropy, the coercive force, the
demagnetizing factor, and the Barkhausen noise parameters of the as-cast and
annealed Fe80V5B15
amorphous alloys was performed. The structural
changes were connected with the temperature range where the
Fe80V5B15
amorphous alloy was characterized by the soft magnetic properties.
PACS numbers: 61.43.Dq, 75.50.Kj, 75.60.Ej
|
EXPERIMENTAL STUDIES OF S=1 HEISENBERG PLANAR ANTIFERROMAGNETIC CHAIN
Ni(C11H10N2O)2Ni(CN)4
E. Cizmára, J. Cernáka,
M. Orendáca, T.
Herrmannsdörferb and A. Fehera
a Faculty of Science, P.J. Safárik University,
Park Angelinum 9, 04154
Ko\v sice, Slovakia
b Physikalisches Institut, Universität Bayreuth, 95440
Bayreuth, Germany
In this paper we discuss the results of experimental studies of
specific heat and magnetic susceptibility of chain compound
Ni(C11H10N2O)2Ni(CN)4.
We have observed a Schottky type anomaly
at T=2.2 K in a temperature dependence of specific heat and the compound was
identified as a S=1 Heisenberg antiferromagnetic chain with the
subcritical
exchange coupling D/kB=5 K, D/|J|=5.2 and the strong in-plane
anisotropy E/kB=2.8 K. It has been found that the in-plane
anisotropy
affects the region of validity of a diluted exciton model [1] and a strong
coupling model [2] for S=1 Heisenberg chains with the strong planar
anisotropy. The analysis suggests that the in-plane anisotropy should be
considered in any attempt to find a compound potentially located in the
boundary of Haldane and ``large-D'' phases.
PACS numbers: 75.40.Cx, 71.20.Be, 75.50.Ee
|
INFLUENCE OF THE LOCAL ENVIRONMENT ON THE MAGNETIC PROPERTIES OF THE
ORDERED Fe1-xAlx ALLOY
J. Deniszczyk
Institute of Physics and Chemistry of Metals, Silesian University Bankowa
12, 40-007 Katowice, Poland
The electronic and magnetic properties of the ordered binary
Fe1-xAlx alloy with the B2 crystal structure
were calculated for Al
concentrations x=0.1875-0.5 using the supercell structure. The
calculations
showed that for increasing Al contents the average magnetization of
Fe1-xAlx falls down rapidly. Upon lowering the unit
cell volume, almost
all configurations of compositions with x >= 0.25 show the abrupt change of
magnetic state from the high moment magnetic state to the low moment
magnetic
state with the moment reduction 0.6-0.8 ”B per atom. The
configurations were found for which the low moment magnetic state solutions
with the antiferromagnetic alignment of magnetic moments of Fe atoms at
antisite positions are stable.
PACS numbers: 71.15.La, 71.15.Fv, 71.20.Lp, 75.50.Bb, 75.30.-m
|
MAGNETIC PROPERTIES OF FERROFLUID WITH COBALT FERRITE PARTICLES
P. Didukha, A. Slawska-Waniewskaa,
J.M. Grenecheb and P.C. Fanninc
a Institute of Physics, Polish Academy of Sciences
Al. Lotników 32/46, 02-668 Warsaw, Poland
b Laboratoire de Physique, UPRESA CNRS 6087,
Université du Maine 72085 Le Mans, France
c Department of Electronic
& Electrical Engineering, Trinity College Dublin 2, Ireland
Low temperature Mössbauer investigations of a diluted magnetic fluid
containing ultrafine CoFe2O4 particles are presented.
The thermal evolution
of cobalt ferrite particles from the magnetically ordered state to the
superparamagnetic state with the blocking temperature at about 80 K, is
shown.
PACS numbers: 75.50.Mm, 76.80.+y, 61.18.Fs
|
AC SUSCEPTIBILITY MEASUREMENTS IN THE INVESTIGATION OF AGGREGATION IN
MAGNETIC FLUIDS
P.C. Fannina and S.W. Charlesb
a Dept. of Electronic & Electrical Engineering,
Trinity College Dublin 2, Ireland
b Dept. of Chemistry, University College of North Wales, Bangor,
LL57 2UW, UK
Measurements of the complex, frequency dependent susceptibility,
chi(omega)=chi '(omega)-ichi''(omega)
of two water based magnetic
fluids, over the frequency range 10 Hz to 1 MHz are reported. Plots of the
susceptibility components against log[f(Hz)] are found to have
approximate
Debye-type profiles with the presence of Brownian relaxation being
indicated
by the frequency, fmax, of the maximum of the loss-peaks in the
chi''(omega) profiles. Corresponding calculations
of particle hydrodynamic radius
indicate the presence of aggregation. Frohlich, normal and lognormal
distribution functions are used to obtain an estimate of the aggregate size
distribution in the samples.
PACS numbers: 75.50.Tt, 76.20.+q
|
JOULE HEATING PREANNEALING EFFECT IN THE COERCIVITY FIELD AND
MAGNETOSTRICTION CONSTANT OF
Co66Fe4Mo2Si16B12 ALLOY
P. Garcia Telloa, J. Gonzálezb,
J.M. Blancoa and R. Zuberekc
a Dpto. Fisica Aplicada I, EUITI, San Sebastián, Spain
b Dpto. Fisica de
Materiales, Facultad de CC Quimicas UPV, San Sebastián, Spain
c Institute
of Physics, Polish Academy of Sciences Al. Lotników 32/46,
02-668 Warszawa, Poland
The effect of thermal treatments (by the Joule heating and
conventional annealing) on the coercivity and saturation magnetostriction constant
in the
amorphous and nanocrystalline
Co66Fe4Mo2Si16B12
alloy is
reported. It is noticeable the near insensibility to the external stress of
coercive field and anisotropy field (leading to extremely low value of
magnetostriction 1.5Ś10^-8) achieved after the Joule heating by two
steps (first one to relax the internal stresses and the second one to
develop a fine nanocrystalline structure).
PACS numbers: 75.50.Kj, 75.30.Gw, 75.80.+q
|
MAGNETOELASTIC ANOMALIES AND SUPPRESSION OF JAHN-TELLER DISTORTIONS IN
La1-xSrxMnO3 BY PULSED MAGNETIC FIELDS
A.M. Kadomtsevaa, Yu.F. Popova,
G.P. Vorob'eva, K.I. Kamilova,
V.Yu. Ivanovb, A.A. Mukhinb and A.M. Balbashovc
a Moscow State University, Leninskie Gori, 119899 Moscow, Russia
b General
Physics Institute of the RAS, 38 Vavilov St., 117942 Moscow, Russia
c Moscow
Power Engineering Inst., 14 Krasnokazarmen St., 105835 Moscow, Russia
Thermal expansion Delta l/l(T) and magnetostriction
lambdaparallel,perp(H,T) in the pulsed
magnetic fields H up to 250 kOe
were studied in the single La1-xSrxMnO3
crystals (x=0.1, 0 .125, and
0.15) at temperatures T=10-320 K. Anomalies in the Delta l/l (T) curves
were observed near a charge (polaron) ordering (Tp) and structural
transitions between orthorhombic Jahn-Teller distorted O' phase and
high
temperature orthorhombic (pseudocubic) O* one (T's).
A noticeable
increase in the field-induced magnetostriction
lambdaparallel,perp(H)
was revealed in the O' phase at Tp<T<T's.
Jumps in the
lambdaparallel,perp(H) curves were
observed at temperatures near
Tp. The observed features may be related to a suppression of the
Jahn-Teller O' phase by the magnetic field and field induced transition
to a new orbital-ordered ferromagnetic state.
PACS numbers: 75.30.Kz, 75.50.Pp
|
XPS STUDY OF ``INFINITE CHAIN''
Ca2CuO3
AND Ca0.5Sr0.5CuO2 COMPOUNDS
I. Jacyna-Onyszkiewicza and
Yu.B. Poltorackyba Institute of
Physics, Adam Mickiewicz University Umultowska 85, 61-614 Poznań,
Poland
b NMO ``Monocrystalreactiv'', Lenin 60, 310077 Kharkov, Ukraine
Al Kalpha excited photoelectron spectra (X-ray photoelectron
spectroscopy) of the O 1s, Cu 2p, Ca 2p, Sr 3d core levels were
measured for ``infinite chain'' Ca2CuO3
and Ca0.5Sr0.5CuO2
compounds. The analysis indicates that for Ca2CuO3
the surface
electronic structure is strongly influenced by a humid atmosphere. The
surface layer is formed predominantly by copper hydroxide. The minor
features
of Cu 2p and O 1s are characteristic of the bulk bonding states. The
valences of the Cu, Ca, and Sr atoms are close to 2+. The core electron
binding energies (\approx 934 eV peak) are due to the
2p3/23d10L1
configuration of Cu(II) ions in the square planar coordination for both
samples.
PACS numbers: 79.60.-i, 74.72.-h, 74.72.Jt
|
INFLUENCE OF LOCAL ENVIRONMENT ON THE ELECTRONIC STRUCTURE AND MAGNETIC
PROPERTIES OF Ni1-xCuxMnSb ALLOYS
A. Jezierskia and A. Szytulaba Institute
of Molecular Physics, Polish Academy of Sciences Smoluchowskiego 17, 60-179
Poznań, Poland
b Institute of Physics, Jagiellonian University,
Reymonta 4, 30-059 Kraków, Poland
The magnetic ordering in Ni1-xCuxMnSb alloys changes from
ferromagnetic (x=0) to antiferromagnetic (x=1). The X-ray and
neutron diffraction showed that the systems crystallise in C1b type
structure. We present an influence of the local chemical ordering on the electronic
and magnetic properties of Ni1-xCuxMnSb alloys. The band
structure and
the magnetic moments were calculated by the spin-polarised linear
muffin-tin
orbital in the atomic sphere approximation method for the experimental values
of the lattice parameters. The magnetic moment of Mn increases from
3.8 ”B for x=0 to 4.18 ”B
for x=1.
PACS numbers: 31.15.Ar, 31.15.Ew, 71.15.Mb,
71.15.-m, 71.15.La, 71.20.-b, 71.20.Be
|
THE MAGNETIC PROPERTIES AND THE BARKHAUSEN NOISE OF THE HYDROGENATED
Fe-V-B AMORPHOUS ALLOY
L. Cenigaa and L. Novákb
a Institute of Experimental Physics, Slovak Academy of Sciences
Watsonova 47, 043 53 Kosice, Slovak Republic
b Department of Physics, Technical
University Komenského park 2, 041 20 Ko\v sice, Slovak Republic
As a consequence of the hydrogenation-dehydrogenation process, in the
present paper the study of structural changes which could be followed by
measuring structure sensitive magnetic properties as the stress induced
anisotropy, the coercive force, the demagnetizing factor, and the Barkhausen
noise parameters of the as-cast and hydrogenated
Fe80V5B15
amorphous alloys is performed.
PACS numbers: 61.43.Dq, 75.50.Kj, 75.60.Ej
|
|