Paramagnetism Heisenberg

Ding, X.-Q., Bominaar, E.L., Bill, E., Winkler, H., Traitwein, A.X., Driieke, S., Chaudhuri, P., and Wieghardt, K. 1990. Mossbauer and electron paramagnetic resonance study of the double exchange and Heisenberg-exchange interactions in a novel binuclear Fe(II/III) delocalized-valence compound. Journal of Chemical Physics 92 178-186. 

An even more quantitative application of VB theory can be developed from the realization that the nearest-neighbor VB model as developed, for example, by Pauling [10], can be mapped exactly onto a Heisenberg spin Hamiltonian [17]. The Heisenberg spin Hamiltonian has long been used to study the interaction between magnetic atoms in transition metal compounds and other paramagnetic substances [18], and can be written most simply as... 

The magnetic coupling between two paramagnetic metal ions is described by the spin Hamiltonian proposed by Heisenberg, Dirac, and Van Vleck (242-245) ... 

Heisenberg exchange between spin-labels and fast relaxing paramagnetic species including dissolved molecular oxygen or transition metals provides a thermal contact with the lattice and is an effective T, mechanism [43]. The effect has been used to measure oxygen concentrations [44]. 

Hyde and Sarna [43] showed that when spin labels collide with fast relaxing paramagnetic species, Heisenberg exchange provides a thermal contact between the slow relaxing species and the lattice. Thus, there is a change in effective This effect has been observed directly by Kusumi et al. [42]. 

Fig. 49. Schematic phase diagrams predicted for the antiferromagnetic order at the surfaces of isotropic Heisenberg magnets (n = 3, upper part) and of XY magnets (n = 2), lower part. Phases occurring are bulk paramagnetic (BP), bulk ferromagnetic (BP), surface paramagnetic (A P), surface ferromagnetic (A P), surface antifcrromagnctic (SAF) and surface spin flop (iSSF). From Binder and Landau (1985).

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