Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals
The formation of both the short-range magnetic order and the electrical conductivity in homogeneously disordered binary crystals under the influence of strong electron correlations is considered (by the example of b.c.c.-Fe1-cCoc alloys). For the description of electron states in a crystal, the mult...
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Repetsky, S.P. Tatarenko, V.A. Melnyk, I.M. Len, E.G. 2014-02-13T20:08:01Z 2014-02-13T20:08:01Z 2010 Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals / S.P. Repetsky, V.A. Tatarenko, I.M. Melnyk, E.G. Len // Український фізичний журнал. — 2010. — Т. 55, № 5. — С. 533-538. — Бібліогр.: 16 назв. — англ. 2071-0194 PACS 71.20.Be, 71.27.+a, 72.10.Bg, 72.10.Di, 72.15.Eb, 75.50.Bb https://nasplib.isofts.kiev.ua/handle/123456789/56194 The formation of both the short-range magnetic order and the electrical conductivity in homogeneously disordered binary crystals under the influence of strong electron correlations is considered (by the example of b.c.c.-Fe1-cCoc alloys). For the description of electron states in a crystal, the multiband model of a tight binding and the method of the cluster expansion for Green’s functions and the thermodynamic potential of a disordered crystal are used. Strong electron correlations and the well-developed short-range order of substitutional atoms lead to the appearance of a quasigap in the electron-energy spectrum. The microscopic mechanisms of magnetic ordering and formation of the electrical resistance are concerned with both the Fermi-level position within the quasigap region and the realignment of the electron-energy spectrum with changes of the temperature or the alloying-component concentration. The parameter of pairwise magnetic correlations decreases with increase in the temperature and tends to zero in a vicinity of the Curie temperature. The nonmonotonic concentration dependence of the Fe-Co-alloy electrical resistance is investigated as well. It is caused by strong electron correlations and the magnetic order resulting from these correlations. Розглянуто формування близького магнiтного порядку та електропровiдностi в однорiдно невпорядкованих бiнарних кристалах пiд впливом сильних електронних кореляцiй (на прикладi сильно корельованої електронної пiдсистеми сплаву ОЦК-Fe1cCoc). Для опису електронних станiв у кристалi використано багатозонну модель сильного зв’язку та метод кластерного розкладання для грiнових функцiй i термодинамiчного потенцiалу невпорядкованого кристала. Сильнi електроннi кореляцiї та “розвинутий” близький порядок атомiв замiщення приводять до появи квазiщiлини в енергетичному спектрi електронiв. Мiкроскопiчнi механiзми магнiтного упорядкування i формування електроопору пов’язанi з розташуванням рiвня Фермi в областi квазiщiлини, а також з перебудовою енергетичного спектра електронiв внаслiдок змiн температури або концентрацiї легуючої компоненти. Параметр парних магнiтних кореляцiй зменшується зi зростанням температури i прямує до нуля в областi температури Кюрi. Дослiджено також немонотонну концентрацiйну залежнiсть електроопору сплаву Fe–Co. Вона визначається сильними електронними кореляцiями та зумовленим ними магнiтним порядком. This work was supported in part by STCU grant #4919 and the N.A.S.U. grant #28=09-H(06). en Відділення фізики і астрономії НАН України Український фізичний журнал Тверде тіло Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals Сильні електронні кореляції в близькому магнітному порядку та електроопорі однорідно невпорядкованих бінарних кристалів Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals |
| spellingShingle |
Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals Repetsky, S.P. Tatarenko, V.A. Melnyk, I.M. Len, E.G. Тверде тіло |
| title_short |
Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals |
| title_full |
Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals |
| title_fullStr |
Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals |
| title_full_unstemmed |
Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals |
| title_sort |
strong electron corrections in short-range magnetic order and electrical resistance of homogeneously disordered binary crystals |
| author |
Repetsky, S.P. Tatarenko, V.A. Melnyk, I.M. Len, E.G. |
| author_facet |
Repetsky, S.P. Tatarenko, V.A. Melnyk, I.M. Len, E.G. |
| topic |
Тверде тіло |
| topic_facet |
Тверде тіло |
| publishDate |
2010 |
| language |
English |
| container_title |
Український фізичний журнал |
| publisher |
Відділення фізики і астрономії НАН України |
| format |
Article |
| title_alt |
Сильні електронні кореляції в близькому магнітному порядку та електроопорі однорідно невпорядкованих бінарних кристалів |
| description |
The formation of both the short-range magnetic order and the electrical conductivity in homogeneously disordered binary crystals under the influence of strong electron correlations is considered (by the example of b.c.c.-Fe1-cCoc alloys). For the description of electron states in a crystal, the multiband model of a tight binding and the method of the cluster expansion for Green’s functions and the thermodynamic potential of a disordered crystal are used. Strong electron correlations and the well-developed short-range order of substitutional atoms lead to the appearance of a quasigap in the electron-energy spectrum. The microscopic mechanisms of magnetic ordering and formation of the electrical resistance are concerned with both the Fermi-level position within the quasigap region and the realignment of the electron-energy spectrum with changes of the temperature or the alloying-component concentration. The parameter of pairwise magnetic correlations decreases with increase in the temperature and tends to zero in a vicinity of the Curie temperature. The nonmonotonic concentration dependence of the Fe-Co-alloy electrical resistance is investigated as well. It is caused by strong electron correlations and the magnetic order resulting from these correlations.
Розглянуто формування близького магнiтного порядку та електропровiдностi в однорiдно невпорядкованих бiнарних кристалах пiд впливом сильних електронних кореляцiй (на прикладi сильно корельованої електронної пiдсистеми сплаву ОЦК-Fe1cCoc). Для опису електронних станiв у кристалi використано багатозонну модель сильного зв’язку та метод кластерного розкладання для грiнових функцiй i термодинамiчного потенцiалу невпорядкованого кристала. Сильнi електроннi кореляцiї та “розвинутий” близький порядок атомiв замiщення приводять до появи квазiщiлини в енергетичному спектрi електронiв. Мiкроскопiчнi механiзми магнiтного упорядкування i формування електроопору пов’язанi з розташуванням рiвня Фермi в областi квазiщiлини, а також з перебудовою енергетичного спектра електронiв внаслiдок змiн температури або концентрацiї легуючої компоненти. Параметр парних магнiтних кореляцiй зменшується зi зростанням температури i прямує до нуля в областi температури Кюрi. Дослiджено також немонотонну концентрацiйну залежнiсть електроопору сплаву Fe–Co. Вона визначається сильними електронними кореляцiями та зумовленим ними магнiтним порядком.
|
| issn |
2071-0194 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/56194 |
| citation_txt |
Strong Electron Corrections in Short-range Magnetic Order and Electrical Resistance of Homogeneously Disordered Binary Crystals / S.P. Repetsky, V.A. Tatarenko, I.M. Melnyk, E.G. Len // Український фізичний журнал. — 2010. — Т. 55, № 5. — С. 533-538. — Бібліогр.: 16 назв. — англ. |
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2025-11-25T23:50:46Z |
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2025-11-25T23:50:46Z |
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| fulltext |
SOLID MATTER
ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 5 533
STRONG ELECTRON CORRELATIONS IN SHORT-RANGE
MAGNETIC ORDER AND ELECTRICAL RESISTANCE
OF HOMOGENEOUSLY DISORDERED BINARY CRYSTALS
S.P. REPETSKY,1 V.A. TATARENKO,2 I.M. MELNYK,2 E.G. LEN2
1Taras Shevchenko National University of Kyiv, Chair of Functional Materials Physics
(2, Academician Glushkov Ave., Kyiv 03022, Ukraine)
2G.V. Kurdyumov Institute for Metal Physics, Nat. Acad. of Sci. of Ukraine,
Department of Solid State Theory
(36, Academician Vernadsky Blvd., Kyiv 03680, Ukraine; e-mail: iramel@ ukr. net )
PACS 71.20.Be, 71.27.+a,
72.10.Bg, 72.10.Di,
72.15.Eb, 75.50.Bb
c©2010
The formation of both the short-range magnetic order and the
electrical conductivity in homogeneously disordered binary crys-
tals under the influence of strong electron correlations is considered
(by the example of b.c.c.-Fe1−cCoc alloys). For the description of
electron states in a crystal, the multiband model of a tight bind-
ing and the method of the cluster expansion for Green’s functions
and the thermodynamic potential of a disordered crystal are used.
Strong electron correlations and the well-developed short-range or-
der of substitutional atoms lead to the appearance of a quasigap
in the electron-energy spectrum. The microscopic mechanisms of
magnetic ordering and formation of the electrical resistance are
concerned with both the Fermi-level position within the quasigap
region and the realignment of the electron-energy spectrum with
changes of the temperature or the alloying-component concentra-
tion. The parameter of pairwise magnetic correlations decreases
with increase in the temperature and tends to zero in a vicinity of
the Curie temperature. The nonmonotonic concentration depen-
dence of the Fe−Co-alloy electrical resistance is investigated as
well. It is caused by strong electron correlations and the magnetic
order resulting from these correlations.
1. Introduction
Strong electron–electron correlations in a crystal influ-
ence significantly the formation of its magnetic and elec-
trical properties. In Fe−Co alloy, the Coulomb in-
teraction between d -electrons is strong, and sequent
strong electron correlations lead to the appearance of
a ’Coulomb’ quasigap in the electron-energy spectrum.
Herewith, the location of the Fermi level within the
quasigap range is concerned with the nature of a weak
temperature dependence of the electrical resistance [1,
2], appearance of spin polarized transport effects, and
high saturation magnetization in Fe−Co alloy [3, 4].
In a given paper, a change of the short-range mag-
netic order with increase in the temperature and a role
of strong electron–electron correlations in the formation
of the concentration dependence of the electrical resis-
tance for b.c.c.-Fe1−cCoc alloys due to the location of
the Fermi level within the ’Coulomb’ quasigap range are
investigated.
2. Theory
For the description of electron states in a crystal, the
multiband tight-binding model and the method devel-
oped in [5] for the cluster expansion of one- and two-
particle Green’s functions and the thermodynamic po-
tential of a disordered-alloy crystal are used. Within the
mentioned method, the coherent potential approxima-
tion [6] is chosen as a zeroth-order one-site approxima-
tion. This approach allows one to consider the electron
scattering by different-kind ion potentials and fluctua-
tions of the spin and charge densities with regard for
correlations in the atom arrangement and orientations
of the localized magnetic moments at respective lattice
sites. The Hamiltonian matrix elements are calculated
within the scope of the Slater–Koster method of linear
combination of atomic orbitals in combination with the
Löwdin orthogonalization procedure [7–9].
The Hamiltonian of the electrons’ and phonons’ sub-
systems of a disordered crystal is determined by the ex-
S.P. REPETSKY, V.A. TATARENKO, I.M. MELNYK et al.
pression
H = H0 +Hint, (1)
where the zeroth-order approximation Hamiltonian, H0,
and the perturbation Hamiltonian, Hint, have the fol-
lowing forms:
H0 = Φ0 +Hph0 +He0, Hint = Hei +Heph +Hee. (2)
Here, H0 consists of the energy of the electrostatic in-
teraction of ions in equilibrium, Φ0, and Hamiltoni-
ans of the subsystems of noninteracting phonons and
electrons, Hph0 and He0, respectively; Hint consists of
the Hamiltonians of electron–ion, electron–phonon, and
pairwise electron–electron interactions, Hei, Heph, Hee,
respectively. Complete expressions for above-mentioned
Hamiltonians within the scope of the Wannier represen-
tation are given in [5].
In our work, within the scope of the mentioned ap-
proach, the calculations of both the concentration de-
pendence of the electrical resistance for b.c.c.-Fe1−cCoc
alloys and the temperature-dependent equilibrium val-
ues of the pairwise magnetic-correlation parameters of
disordered b.c.c.-Fe0.5Co0.5 alloy are performed. The
equilibrium values of parameters of magnetic and inter-
atomic correlations are obtained from the condition that
the free energy is minimal.
The free energy, F , as a function of the system vol-
ume (V ), temperature (T ), number of electrons (Ne),
and parameters of both the interatomic correlations and
the correlations in an orientation of localized magnetic
moments is defined in terms of the thermodynamic po-
tential, Ω, by the relation [5]
F = 〈Φ0〉 − TSc + Ω0e + Ω0ph + Ω′ + εF 〈Ne〉. (3)
Here, Ω0e – the thermodynamic potential of noninter-
acting electrons; Ω0ph – the thermodynamic potential
of noninteracting phonons; Ω′ – the thermodynamic po-
tential contribution which is caused by the processes of
electrons’ and phonons’ scatterings in a disordered crys-
tal; εF – the chemical potential of electrons; 〈Φ0〉 – the
average value of electrostatic interaction energy of ions;
Sc – the configuration entropy of ions’ subsystem. The
configuration contribution, Sc, is explicitly determined
by parameters of a short-range atomic order [5]. More-
over, the contribution of the electron subsystem depends
on the parameters of short-range atomic and magnetic
orders by means of the one-particle Green’s function of
the electron subsystem. This function determines the
electron density of states as well.
Within the two-center cluster approximation, the elec-
tron density of states has the form [5]
ge(ε) = − 1
Nπ
ImSp〈G(ε)〉 =
=
1
ν
∑
i,γ,σ,λ,mλ0iγ
P
λ,mλ0iγ
0i g
λ,mλ0iγ
0iγσ (ε), (4)
where ε – the energy parameter; 〈G(ε)〉 – the configu-
ration averaged Green’s function of electrons; ν – the
number of sites within a conditional unit cell; N – the
total number of lattice sites; Pλ,mλniγ0i – the probability
to find a λ-kind atom with the localized magnetic mo-
ment mλniγ at the site (ni), where the first index, n, in
a bracket numbers a conditional cell in a crystal, and
the second index, i, indicates the number of a sublat-
tice in this conditional cell; gλ,mλ0iγ
0iγσ (ε) – the conditional
partial electron density of states for the energy band γ
with the projection of spin σ, which is defined by one-
particle Green’s functions and by means of the condi-
tional probabilities to find localized magnetic moments
and different-kind atoms at the nearest sites of a crys-
tal lattice under condition that, at the site (0i), there
is a λ-kind atom with the localized magnetic moment of
electrons mλ0iγ [2].
The Fermi level, εF , of electrons in a crystal is defined
by the formula [5]
〈Z〉 =
∞∫
−∞
f(ε, εF )ge(ε)dε. (5)
Here, 〈Z〉 is the average number of electrons per atom;
and f(ε, εF ) is the Fermi function.
The localized magnetic moment mλni is defined by the
difference between conditional partial electron densities
of states with different spin projections at the given site:
mλni =
∑
γ
mλniγ ,
mλniγ =
∞∫
−∞
f(ε, εF )(gλ,mλniγniγσ (ε)− gλ,mλniγniγ−σ (ε))dε. (6)
Let the localized magnetic moment have only two pro-
jections on a quantization axis: mλni = µ↑λni (up), µ↓λni
(down), and let their values be determined by both the
electron–electron interaction and the kind of an atom at
534 ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 5
STRONG ELECTRON CORRELATIONS IN DISORDERED CRYSTALS
Fig. 1. Electron density of states of b.c.c.-Fe0.5Co0.5 alloy with
equilibrium parameters of atomic and magnetic orders at 300 K
(—) and 500 K (- - -)
the given site. Equilibrium values of the local character-
istics of the magnetic structure are determined by means
of the minimization of the free energy by the parameter
of pairwise magnetic correlations, ε
mµ↑λn1i1
µ↑
λ′n2i2
n1i1n2i2
, in the
whole definition interval of it. The parameter of pairwise
magnetic correlations is concerned with the conditional
probability, P
µ↑λn1i1
/µ↑
λ′n2i2
n1i1n2i2
(i.e. the probability to find
a localized magnetic moment µ↑λn1i1
at the site (n1i1)
under condition that a magnetic moment µ↑λ′n2i2
is lo-
calized at the site (n2i2)), by the formula [10]
ε
mµ↑λn1i1
µ↑
λ′n2i2
n1i1n2i2
= P
µ↑
λ′n2i2
n2i2
(P
µ↑λn1i1
/µ↑
λ′n2i2
n1i1n2i2
− P
µ↑λn1i1
n1i1
).
(7)
Expressions (4)–(7) describe the interrelation between
the magnetic-order formation in an alloy and its elec-
tronic structure.
The exact expression for the static electrical conduc-
tivity of an alloy, σαβ , was derived in [2] as follows:
σαβ = − e2~
NΩ0
∞∫
−∞
dε(−∂f(ε, εF )
∂ε
)×
×Sp〈υα(G(ε+)−G(ε−))υβ(G(ε+)−G(ε−))〉. (8)
Here, G(ε±) ≡ G(ε ± iδ) = (ε± −H)−1 is the retarded
(’+’) or advanced (’−’) Green’s function of an alloy
crystal, H – the one-electron Hamiltonian of an alloy,
δ → +0; G = G̃+ G̃T̂ G̃, where G̃ – the Green’s function
Fig. 2. Temperature dependence of equilibrium values of the pair-
wise magnetic-correlation parameter εm for b.c.c.-Fe0.5Co0.5 alloy
for the effective medium, T̂ – the matrix of electron scat-
tering by the random potential; υα – the α-component
of the electron velocity vector operator; Ω0 – the prim-
itive unit-cell volume; e – the electron charge; ~ – the
Planck’s constant; the brackets 〈...〉 denote the configu-
ration averaging.
3. Numerical Results
The Hamiltonian matrix elements calculated for the Fe–
Co alloy within the scope of the Slater–Koster method
determine values of the atomic scattering potentials for
d-electrons which are equal to 0.04 (in units of a respec-
tive band width, wd) by order of magnitude. At the
same time, the estimation of the parameter, Ud, of the
Coulomb interaction between d-electrons at the one site
shows that the strong electron-correlation regime takes
place in the given system, because Ud/wd ∼ 0.55. In
this case, the splitting of energy bands (for d-electrons)
in the Fe–Co alloy is caused by the Coulomb interac-
tion between electrons more than by its scattering on
the crystal potential.
Phase transitions of alloys with strong electron corre-
lations are caused by changes of an electronic structure.
The realignment of the electron-energy spectrum occurs
with changing the temperature (Fig. 1). An increase
in the temperature leads to a ’tailing’ of the ’Coulomb’
energy quasigap on the curve of the electron density of
states due to the scattering of electrons by vibrations
of the crystal lattice (i.e. electron–phonon interaction).
An increase in the temperature leads also to the damp-
ing of the correlations in an orientation of the magnetic
moments or, in other words, to a decrease of the param-
ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 5 535
S.P. REPETSKY, V.A. TATARENKO, I.M. MELNYK et al.
Fig. 3. Electron density of states of b.c.c.-Fe1−cCoc alloys with
equilibrium values of atomic and magnetic orders at different val-
ues of concentration, c
eter of pairwise magnetic correlations (Fig. 2) up to zero
at a temperature of ∼= 1200 K, which is close to the ex-
perimental values of the Curie temperature (TC ∼= 1250
K) for FeCo alloy [11, 12]. In the presented results of
numerical calculations, the short-range magnetic order
is determined by the parameter of pairwise correlations
in an orientation of magnetic moments at the first coor-
dination sphere only, εm ≡ ε
mµ↑λ01µ
↑
λ′m2
01m2 . Note that the
equilibrium values of εm correspond to the ferromagnetic
phase (i.e. εm > 0).
A change of the chemical composition of an alloy leads
to a change of the partial contributions of alloy’s com-
ponents to the electron density of states (Fig. 3). At
the same time, according to expression (6), the values of
localized magnetic moments and the density of states at
the Fermi level within the energy quasigap change that
influences the formation of conductivity (8) of a binary
alloy with strong electron correlations.
The concentration-dependent electrical resistance of
b.c.c.-Fe1−cCoc alloys at a temperature of 300 K is pre-
sented in Fig. 4,a. For the comparison, the experimen-
tal values of b.c.c.-Fe1−cCoc resistivity [13] are given in
Fig. 4,b.
The results of computations conform qualitatively to
the experimental data [13]. The lack of a quantitative
coincidence of computed electrical-resistance values and
respective experimental ones may be explained in part by
the concentration heterogeneity of the investigated alloys
[14] and their multiphase structure [15] which are not ac-
countable yet in the presented numerical computations.
Moreover, excepting the above-mentioned imperfections
Fig. 4. Concentration dependences of resistivity, ρ = 1/σzz , for
b.c.c.-Fe1−cCoc alloys at T = 300 K: a – computation results
according to (5); b – experimental values [13]
of a crystal structure, there is the additional factor which
is not taken into account in our theoretical model and,
nevertheless, is crucially important for the atomic order-
ing of alloys into the B2-type superstructure. This is the
tendency of the investigated alloys to their decomposi-
tion into the antiphase domains of the B2-type atomic
order. Boundaries of such domains cause the additional
scattering of conduction electrons and the corresponding
enhancement in values of the experimentally measured
electrical resistance of a real sample in comparison with
ones for a homogeneously (dis)ordered alloy.
As revealed by means of the analysis of the con-
centration dependence of the b.c.c.-Fe1−cCoc electri-
cal resistance in the view of the electron-energy spec-
trum realignment, a change of the electrical conductiv-
ity has a weak dependence on the atomic-order degree.
This is confirmed by the presence of minima in the ex-
perimental concentration dependences of resistance for
536 ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 5
STRONG ELECTRON CORRELATIONS IN DISORDERED CRYSTALS
Fig. 5. Concentration dependences of the averaged localized mag-
netic moments (a) and the electron density of states at the Fermi
level (b) for b.c.c.-Fe1−cCoc alloys
the equiatomic composition at high temperatures (i.e.
higher than the order–disorder transition point), as well
as at low temperatures [16]. At the same time, the
magnetic-subsystem state is a distinct governing fac-
tor. The nonmonotonic concentration dependence of
the Fe−Co-alloy electroresistance is caused by both the
strong electron correlations and the magnetic order re-
sulting from these correlations. Strong correlations be-
tween electrons lead to the appearance of the ’Coulomb’
quasigap in the electron-energy spectrum of a binary al-
loy. The Fermi-level position in the quasigap range de-
termines the electrical conductivity of an alloy. A de-
crease of the averaged localized magnetic moments (Fig.
5,a) and an increase of the electron density of states
at the Fermi level in the energy spectrum (Fig. 5,b)
lead to a decrease of the electrical resistance of an alloy
with strong electron correlations. The opposite change
of above-mentioned parameters of state leads to an in-
crease of the electrical resistance.
4. Conclusions
The microscopic mechanisms of magnetic ordering in a
Fe0.5Co0.5 alloy and formation of the electrical resistance
of b.c.c.-Fe1−cCoc alloys concern with both the Fermi-
level position within the ’Coulomb’ quasigap range in
the electron-energy spectrum and the realignment of this
spectrum.
The values of parameters of the pairwise magnetic cor-
relations decrease with increase in the temperature that
allows one to estimate the Curie temperature of the alloy
under study (for Fe0.5Co0.5, TC ∼= 1200 K).
The nonmonotonic concentration dependence of the
Fe–Co-alloy electroresistance is conditioned by strong
electron correlations and the magnetic order resulting
from these correlations to a greater extent than by the
atomic-order degree.
This work was supported in part by STCU grant ]4919
and the N.A.S.U. grant ]28/09−H(06).
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Received 18.09.09
СИЛЬНI ЕЛЕКТРОННI КОРЕЛЯЦIЇ В БЛИЗЬКОМУ
МАГНIТНОМУ ПОРЯДКУ ТА ЕЛЕКТРООПОРI
ОДНОРIДНО НЕВПОРЯДКОВАНИХ
БIНАРНИХ КРИСТАЛIВ
С.П. Репецький, В.А. Татаренко, I.М. Мельник, Є.Г. Лень
Р е з ю м е
Розглянуто формування близького магнiтного порядку та еле-
ктропровiдностi в однорiдно невпорядкованих бiнарних кри-
сталах пiд впливом сильних електронних кореляцiй (на при-
кладi сильно корельованої електронної пiдсистеми сплаву
ОЦК-Fe1−cCoc). Для опису електронних станiв у кристалi ви-
користано багатозонну модель сильного зв’язку та метод кла-
стерного розкладання для грiнових функцiй i термодинамiчно-
го потенцiалу невпорядкованого кристала. Сильнi електроннi
кореляцiї та “розвинутий” близький порядок атомiв замiщення
приводять до появи квазiщiлини в енергетичному спектрi еле-
ктронiв. Мiкроскопiчнi механiзми магнiтного упорядкування
i формування електроопору пов’язанi з розташуванням рiвня
Фермi в областi квазiщiлини, а також з перебудовою енергети-
чного спектра електронiв внаслiдок змiн температури або кон-
центрацiї легуючої компоненти. Параметр парних магнiтних
кореляцiй зменшується зi зростанням температури i прямує до
нуля в областi температури Кюрi. Дослiджено також немоно-
тонну концентрацiйну залежнiсть електроопору сплаву Fe–Co.
Вона визначається сильними електронними кореляцiями та зу-
мовленим ними магнiтним порядком.
538 ISSN 2071-0194. Ukr. J. Phys. 2010. Vol. 55, No. 5
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