Spin-Wave Excitation in Cubic Rare-Earth Compounds

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Abstract
Some of the cubic rare‐earth compounds are ferromagnetic at low temperatures. However the observed magnetic moment is much smaller than it is for the free ion, because of the effect of the strong crystalline field on the trivalent rare‐earth ions. Solving the one‐ion Hamiltonian numerically, we construct approximate ferromagnetic spin wave states of an unusual nature, in that they involve ionic states of orbital as well as spin angular momentum in both a crystalline and an exchange field. From the excitation spectrum of these states, we calculate the temperature dependencies of the specific heat, strong‐field susceptibility, and g factor of a ferromagnetic array of trivalent rare‐earth ions, and attempt to predict the behavior of HoN and TbN.