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Green's Function Theory of a Heisenberg Ferromagnet with Strong Dipole-Dipole Interactions: Magnetization of Gd Cl 3

1970; American Physical Society; Volume: 1; Issue: 1 Linguagem: Inglês

10.1103/physrevb.1.314

0556-2805

Egon Becker, Michael Plischke,

Magnetic properties of thin films

We have investigated the magnetization as a function of $T$ and $H$ of a spin system with both isotropic Heisenberg exchange and dipole-dipole interactions for $S\ensuremath{\ge}\frac{1}{2}$ and a hexagonal crystal structure. The Green's functions for such a system, recently derived by Becker, are decoupled in a first-order random-phase approximation. For both Heisenberg-dipole and simple-dipole crystals, we find a lowering of the magnetization below saturation at $T=0$. The Curie-Weiss temperature $\ensuremath{\theta}$ and the ordering temperature ${T}_{c}$ are calculated and compared with experimental values on Gd${\mathrm{Cl}}_{3}$. In the limit of zero exchange, we obtain a condition for the type of lattice and shape of domains which make ferromagnetic ordering possible.