MAGNETIC TRANSLATIONS FOR A SPATIALLY PERIODIC MAGNETIC FIELD
W. Florek
Computational Physics Division, Institute of Physics, A.
Mickiewicz
University Umultowska 85, 61-614 Poznań, Poland
Received: November 29, 1999
It is shown that in the case of a free electron in a spatially
periodic
magnetic field the concept of magnetic translations operators is still
valid
and, moreover, these operators can be defined in the same way as for a
Bloch
electron in a uniform magnetic field. The results can be a useful tool
in the
investigation of recently observed phenomena in 2D electron gas with
spatially modulated density.
PACS numbers: 02.20.-a, 73.40.Hm, 71.70.Di, 71.10.-w
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KINETIC ENERGIES IN THE DIRECT DOUBLE PHOTOIONIZATION OF HELIUM AND
THE ELECTRON-ELECTRON CORRELATION
J. Bauer
Katedra Fizyki Jadrowej i Bezpieczeństwa Radiacyjnego Uniwersytetu
Lódzkiego, Pomorska 149/153, 90-236 Lódz, Poland
Received: October 28, 1999
We present a simple model describing kinetic energy probability
distributions of outgoing electrons in the direct double photoionization
of
helium. The model applies to photons of energy greater than the binding
energy of the atom and to radiation intensities extending from
perturbation
regime to the strong-field one. It appears that the shape of probability
distribution is mainly determined by the electron-electron correlation
in
their final state. For nonperturbative intensities the distribution
depends
strongly on polarization of incident radiation.
PACS numbers: 32.80.Rm, 33.80.Rv
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ULTRASONIC WAVES IN MAGNETIC LIQUIDS: TWO-PHASE APPROACH AND
EXPERIMENTAL RESULTS
M. Kaczmareka, T. Hornowskib, A. Skumielb
and M. Labowskib
a Department of Environmental Mechanics Pedagogical University in
Bydgoszcz Chodkiewicza 30, 85-064 Bydgoszcz, Poland
b Institute of
Acoustics Adam Mickiewicz University Umultowska 85, 61-614 Poznań,
Poland
Received: September 6, 1999; revised version November 29, 1999; in final
form February 2, 2000
A two-phase model of dynamical behavior of magnetic liquid
influenced
by constant magnetic field is considered. The model takes into account
mutual
interaction of clusters giving skeleton's stiffness and interaction of
clusters with free liquid producing attenuation and dispersion of waves
for
transversally isotropic system. Rotational degrees of freedom are
disregarded. Predictions of the model are discussed for variable amount
of
clusters and compared with experimental data for different magnetic
fields.
PACS numbers: 47.35.+i, 75.50.-y, 62.60.+v
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EFFECTIVE PAIR INTERACTION FROM AB INITIO PSEUDOPOTENTIALS -
IMPORTANCE AND APPLICATIONS
S. Haldar
Condensed Matter Physics Research Centre, Physics Dept. Jadavpur
University, Calcutta - 700 032, India
A. Sarkar
B.K. Girls' College, Howrah 711101, India
and D. Sen
Barasat Govt. College, Barasat 743201, West Bengal, India
Received: August 12, 1999; in final form January 12, 2000
Computation of reliable effective interionic pair interaction for
simple metals has been discussed on the basis of localised ab initio
pseudopotential within linear screening approximation. The influence of
different commonly used screening functions on the shape of pair
potential is
examined and the temperature dependence of the interaction is also
investigated. Various features of the potential are studied and compared
with
empirical and available first principle results. Importance of the
present
study and some related problems are also analysed.
PACS numbers: 63.10.+a, 65.90.+i
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STRUCTURAL STUDY OF
(NH4)4H2(SeO4)3
IN THE LOW-TEMPERATURE PHASE
T. Fukami, N. Higa
Department of Physics and Earth Sciences, Faculty of Science University
of the Ryukyus, Okinawa 903-0213, Japan
and R.H. Chen
Department of Physics, National Taiwan Normal University Taipei,
Taiwan, 117, Republic of China
Received: October 7, 1999, revised version December 21, 1999
The crystal structure of tetraammonium dihydrogen
triselenate, (NH4)4H2(SeO4)3,
in the low-temperature
phase at 141 K is studied by X-ray diffraction. The space group symmetry
(triclinic P1) and the structure parameters are determined. By the shift
of the Se atom from the center of the SeO4 tetrahedron, it is suggested
that
the (NH4)4H2 (SeO4)3
crystal in the low-temperature phase is
ferroelectric with the electric dipole moment along the c-axis. The
rotation of the SeO4 tetrahedron suggested by electron paramagnetic
resonance measurements is discussed.
PACS numbers: 61.66.Fn, 64.60.Fr
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A GREEN FUNCTION ESTIMATION OF CORRECTION TO VEGARD'S LAW FOR
ISOVALENT
SUBSTITUTIONAL DEFECTS IN ALKALI HALIDE CRYSTALS
S. Datta Roy (Paul)a and S.K. Dasb
a Department of Physics, Bethune College, Calcutta 700 006,
India
b Azad Physics Centre, Department of Physics Maulana Azad
College, Calcutta 700 013, India
Received: October 25, 1999; revised version January 25, 2000
A Green function method is developed for estimation of lattice
parameter r(chi) of an AX-BX solid solution over entire
composition range (chi=0 to 1). The r(chi) obtained in the present
method is different from the value rV(chi) suggested by Vegard's
law.
We estimated the deviation from Vegard's law, r(chi)-rV(chi),
over
entire composition range for isovalent substitutional defect in alkali
halide
crystals. When compared to X-ray diffraction measurements, we find that
the
deviation is in correct direction, variation of r(chi) with chi is
consistent with experiment and the overall agreement is fairly good
considering the accuracy of the experiment.
PACS numbers: 61.72.Bb, 61.82.Bg
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NUCLEATION AND CRYSTAL GROWTH OF Cu ON Ir TIPS UNDER ULTRA-HIGH
VACUUM AND IN THE PRESENCE OF OXYGEN
S.M. Zuber and A. Ciszewski
Institute of Experimental
Physics, University of Wroclaw pl. Maxa Borna 9, 50-204 Wroclaw,
Poland
Received: November 19, 1999
Results concerning the morphology of Cu adsorption layers
deposited
from vapor under ultrahigh vacuum on Ir tip and the influence of
oxygen on
this morphology are reported. The method employed was field electron
emission
microscopy. It was found that the presence of oxygen decreases the
copper
wettability of iridium. Preadsorption of oxygen on the Ir surface is
followed
by an increase in cohesion interaction between atoms of the Cu deposited
onto
the tip at room temperature. Coadsorption of Cu and O on the Ir tip
surface
at liquid nitrogen temperature, when followed by gradually heating the
adlayer, results in crystallization of the deposit in the temperature
range
from 430 K to about 700 K. Some evidence indicates the formation of
Cu2O
with a high degree of crystallinity under these conditions. Cu and O
coadsorption on the Ir surface at a temperature higher than 1090 K leads
to
selective accumulation of Cu on the {111} faces and to formation of
epitaxial crystals which are oriented to the substrate in the same
manner as
the Cu crystals grown at ultra-high vacuum from Cu flux containing no
oxygen.
Oxygen incorporated into the Cu beam interact preferentially with {011}
and
{001} Ir faces, where it can produce oxide layers.
PACS numbers: 61.16.Fk, 81.15.Ef, 68.35.Bs
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THERMODYNAMIC PROPERTIES OF D-WAVE PAIRED SUPERCONDUCTORS IN THE LOW
TEMPERATURE AND SUBCRITICAL REGIONS
W. Kumala, R. Gonczarek and M. Mulak
Institute of Physics, Wroclaw University of Technology Wybrzeze
Wyspiańskiego 27, 50-370 Wroclaw, Poland
Received: May 11, 1999; revised version October 13, 1999; in final form
February 11, 2000
D-wave paired isotropic Fermi system in the limiting cases
T -> Tc and T -> 0 is considered. Values of the
energy
gap, the thermodynamic potential, and the specific heat as a function of
temperature are given for admissible solutions and compared with values
for S-wave paired system. It is shown that the linear term of low
temperature
specific heat vanishes likewise in case of S-wave pairing. The obtained
results make prospects to define the geometry of the energy gap in
virtue of
the behavior of the specific heat in the limiting temperature cases for
heavy-fermion superconductors.
PACS numbers: 74.20.-z
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PECULIAR PROPERTIES OF ULTRATHIN FCC IRON FILMS EPITAXIALLY GROWN ON
Cu(001)
R. Wojneckia and A.
Sukiennickia,b
a Institute of Physics, Polish Academy of
Sciences Al. Lotników 32/46, 02-668 Warsaw, Poland
b Faculty of
Physics, Warsaw University of Technology Koszykowa 75, 00-662 Warsaw,
Poland
Received: November 3, 1999
Very peculiar electronic structure and local magnetic moment
distribution for fcc Fe ultrathin films of 1, 2, 3, and 4 monolayers of
thickness, epitaxially grown on Cu(001) substrates and covered with some
layers of Cu, are calculated. The lattice constant of the Fe film is
assumed
to be equal to that of Cu, homogeneously in the whole film. The
competition
between the surface ferromagnetism and bulk antiferromagnetism results
in ferromagnetism of 2-monolayer film, asymmetric solution for 3-monolayer
film
and antisymmetric solution for 4-monolayer film.
PACS numbers: 75.70.Ak
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PHASE TRANSITIONS IN MAGNETIC AND SUPERCONDUCTING SYSTEMS WITH
FLUCTUATING VALENCE. CHEMICAL POTENTIAL EVIDENCE
E. Goslawskaa, M. Matlaka and Kh. Eidb
a Institute of Physics, Silesian University Uniwersytecka 4, 40-007
Katowice, Poland
bPhysics Department, Faculty of Education Ain-Shams
University, Roxy, Cairo, Egypt
Received: November 18, 1999
We investigate the critical behaviour of the chemical potential
and
average occupation numbers using the extended s -f model with intersite
Cooper pairing for systems with fluctuating valence. The model is able
to
describe phase transitions from normal ferromagnet to normal paramagnet
at
T=TC, from superconducting paramagnet to normal paramagnet at
T=TS, as well as reentrant phase transitions with three critical
temperatures TS1, TC and TS2
(TS1 < TC < TS2).
Present investigation, as well as recent results
obtained for another models suggest one-to-one correspondence between
critical temperatures of the system and kinks appearing in the
temperature
dependence of the chemical potential and average occupation numbers.
This, in
turn, indicates a possibility to apply the measurement of the chemical
potential vs. temperature as an experimental universal tool when looking
for phase transitions in solids.
PACS numbers: 75.30.Kz, 75.40.Cx
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MAGNETIC SUSCEPTIBILITY DISACCOMMODATION AND MÖSSBAUER EFFECT IN
MICROCRYSTALLINE Fe-Si RIBBONS
W.H. Ciurzyńska
Institute of Physics, Technical University of Czestochowa Al. Armii
Krajowej 19, 42-200 Czestochowa, Poland
Received: November 30, 1999 In memory of Professor Jerzy Wojciech Moroń
The magnetic susceptibility disaccommodation of the
microcrystalline
Fe-xSi (x=3, 5, 6.5, and 7.2 wt%) ribbons in the as-quenched state
and after annealing at 1370 K for 1 h was investigated in the temperature
range
from 220 to 410 K. Simultaneously, the microstructure of those samples
was
studied using the Mössbauer spectroscopy. It is found that the
isochronal
disaccommodation curves may be decomposed into five elementary
processes.
Taking into account the results obtained from the Mössbauer spectra
analysis, the relaxational process with activation energy equal to
0.84 eV
may be considered as the Snoek relaxation. However, the relaxational
processes of higher activation energy seem to be connected with jumps of
C atoms in the vicinity of Fe atoms surrounded by 1, 2, 3, and 4 silicon
atoms.
PACS numbers: 75.60.Lr, 76.80.+y
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