A model for induced moment ferromagnetism in some praseodymium-transition metal compounds

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Abstract
The cubic Laves PrT2 compounds, where T is a metal atom, are ferromagnets which display a variety of magnetic moments on the Pr3+ ion varying from 0.61 mu B to 2.2 mu B. Crystal field analysis shows that the free Pr3+ ion in some of these compounds must be in a singlet ( Gamma 1) state. Here the authors analyse a singlet-triplet model for Pr3+ in which the induced moments interact with an enhanced d band in the compound. Expressions are given for the zero temperature magnetization and the Curie temperature in this model and the spin dynamics are discussed. In particular it is shown that the lowest spin modes are paramagnons or spin waves typical of an itinerant paramagnet or ferromagnet respectively. Finally in agreement with Fulde (1972) none of the excitonic modes become soft at the transition point.

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