Magnetism: mean-field approach

Here fictitious spin with the eigenvalues a = -1 for the LS state and a = +1 for the HS state. The postulated Hamiltonian formally describes an Ising-like system under the external field At. Unlike true magnetic systems, the degeneracies of the two levels are different thus the suffix Ising-like. Within the mean field approach the single molecule can be characterised by the Hamiltonian... 

The dependence of the magnetic properties of amorphous R-3d alloys on temperature and composition is most conveniently described by means of a mean field approach (Hasegawa, 1975 Heiman et al., 1976 Gangulee and Taylor, 1978 Gangulee and Kobliska, 1978 Taylor and Gangulee, 1980 Hansen and Urner-Wille, 1979). For a system consisting of n different components in which x, is the atomic... 

Within a mean-field approach the R-T exchange interaction is described by molecular fields that are aeting on the magnetic moments. In a two-sublattice model, the suitable effective molecular fields acting on the R and T moments can be written as... 

If we understand FM or magnetic properties of quark matter more deeply, we must proceeds to a self-consistent approach, like Hartree-Fock theory, beyond the previous perturbative argument. In ref. [11] we have described how the axial-vector mean field (AV) and the tensor one appear as a consequence of the Fierz transformation within the relativistic mean-field theory for nuclear matter, which is one of the nonperturbative frameworks in many-body theories and corresponds to the Hatree-Fock approximation. We also demonstrated... 

De Jongh showed that in 2-D systems, spin-reduction can also be deduced from the perpendicular magnetic susceptibility7,269. The experimental value of xi extrapoled to 0 K is in good agreement with the theoretical value obtained by means of the spin-wave theory (Xi (0). The difference between the latter value and that calculated via the molecular field approach Xkmf) is essentially due to the zero-point spin reduction. 

A different approach to obtain the mean-field parameters from experimental magnetization data is presented here, based on data scaling. A summarized version of this work has been published in 2007 (Amaral et al., 2007). We consider the general mean field law, M(H, T) = f (H + )/T), where the state function / is not pre-determined, and that A (as in =... 

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