Local moment magnetism of fcc FeNi alloys II. Ising approximation Monte Carlo

Mössbauer analysis and magnetic properties of Invar Fe–Ni–C and Fe–Ni–Mn–C alloys

“…Fe-Ni alloys: the ferromagnetic (FM) Fe-Ni and Ni-Ni and the antiferromagnetic (AF) Fe-Fe interspin interactions. This is qualitatively consistent with the data of [15,16]. The addition of C saves the mixed character of interspin interactions by weakening the Ni-Ni FM and increasing the Fe-Ni FM and Fe-Fe AF interspin interactions (Table II).…”

“…The broadened distribution of fields is attributed to fluctuations of spin density at Fe nuclei in different atomic configurations of Fe with C and Ni (Mn). The asymmetric shape of the spectra is due to the wide distribution of Signs of J NiNi (r i ) < 0, J FeFe (r i ) > 0, J NiFe (r i ) < 0 are opposite to those obtained in [15,16] that is associated with the initial definition of the exchange interaction energy and remains the correct determination of FM and AF ordering. isomer shifts, p(δ) [13].…”

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

“…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.…”

“…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.…”

Invar Behavior in Fe-Ni Alloys is Predominantly a Local Moment Effect Arising from the Magnetic Exchange Interactions Between High Moments

“…In a series of papers (Dang et al, 1995;Dang and Rancourt, 1996;Grossmann and Rancourt, 1996) culminating in the description of the local moment frustration model , we have shown by various mean field theory and Monte Carlo calculations that a simple HM local moment model, with fixed moment magnitudes on Fe and Ni, three constant exchange parameters for Fe-Fe, Fe-Ni, and Ni-Ni pairs, and one non-zero constant magnetovolume coupling parameter, J 0 Fe-Fe ¼ @J Fe-Fe =@r, for Fe-Fe pairs, can reproduce the composition and temperature dependencies of all the physical properties of interest: saturation magnetization and deviation from the Slater-Pauling curve, thermal expansion, Curie point, spontaneous volume change, paraprocess high-field magnetic susceptibility, chemical order-disorder effects, bulk modulus, magnetic specific heat, etc. This simple model, with only four adjustable parameters, gives good qualitative agreement and at worst correct orders of magnitudes in the entire range 0 to $ 65 apc Fe and at all relevant temperatures, provided the Fe-Ni and Ni-Ni exchange interactions are relatively large and positive (i.e., ferromagnetic), the Fe-Fe exchange interaction is somewhat smaller and negative (antiferromagnetic), and @J Fe-Fe =@r is large and positive (þ10 4 K/Å , with the Hamiltonian used by Rancourt and Dang (1996)).…”