Magnetism in systems with reduced dimensionality and chemical disorder: The local environment effects

Interatomic Interactions in F.C.C.-Ni–Fe Alloys

“…Fourier components of these energies, Fig. 5) are conditioned by the changes in L Ni value at these concentrations and probably correspond to transition of electron subsystem of Fe atoms from one electronic state to another or to transition to the state of coexistence of two and more equilibrium electronic states that, by-turn, testifies to the probable presence of two γ-states [18][19][20][21][22][23][24]66] of Fe atoms in appropriate composition region.…”

“…Many theoretical investigations [15][16][17][18][19][20][21][22][23][24][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81] have been devoted to studies of effects of ferro-and (or) antiferromagnetic order in alloys with atomic LRO (SRO). Conditionally, all these theories and models can be divided into two groups: (i) models, which are based on the primary contribution of itinerant electron magnetism [64,75,76] to magnetism of an alloy, and (ii) so-called local magnetic moment model [66][67][68], which implies the carriers of uncompensated magnetic moments as atoms located at the effectively-periodic lattice sites.…”

“…Conditionally, all these theories and models can be divided into two groups: (i) models, which are based on the primary contribution of itinerant electron magnetism [64,75,76] to magnetism of an alloy, and (ii) so-called local magnetic moment model [66][67][68], which implies the carriers of uncompensated magnetic moments as atoms located at the effectively-periodic lattice sites. As for magnetism of f.c.c.-Ni-Fe alloys, the basic complexity for developing such quantitative model is the simultaneous quantification of, firstly, the magnetism of both constituents of an alloy (Ni and Fe), secondly, the significant difference between Ni and Fe magnetic moments, and, thirdly, the availability of two magnetic states of Fe atoms, namely, two so-called Weiss γ-states [18][19][20][21][22][23][24]66], namely, the low-spin (LS) and high-spin (HS) states. There are some methods and approaches for definition of 'exchange' 'integrals' for magnetic interactions in alloys, in particular, MSCF (or MF) approximations [69][70][71][72][73][74]77], cluster methods in the mean-field theory [79], Monte Carlo Ising-type approximation [80], ab initio models [18-24, 75, 76], etc.…”

“…2) at c > 0.55 is apparently conditioned by both the presence of heterogeneous (atomic and/or magnetic) states [14][15][16][17][18][19][20][21][22][23][24]66] in f.c.c.-Ni-Fe alloys and the simultaneously increasing contribu-tion of itinerant electron magnetism into 'effective' 'exchange' interactions [75,76]. In general case, in the measurands such as T C (c) (25), there is a combination of all parameters such as follow:…”

“…In a concentration region of Fe atoms, 0.45 < c < 0.55, Elinvars are formed (with atomic long-rangeordered L1 0 -CuAuI-type (NiFe) layered structure with temperature factor of electrical resistance possessing high values) [2]. A special attention should be paid to Fe-Ni Invars [1-3, [18][19][20][21][22][23][24] with relative concentration of Fe atoms close to c ≅ 0.65. Near this chemical composition, such an alloy has microheterogeneous structure, which may be probably atomic long-range-ordered of L1 2 -Cu 3 Au type (Fe 3 Ni) in part.…”