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The transition region from paramagnetism to ferromagnetism of the transition metals and their alloys

1972; Wiley; Volume: 50; Issue: 2 Linguagem: Inglês

10.1002/pssb.2220500227

1521-3951

E. Vogt,

Rare-earth and actinide compounds

Abstract The terms “nearly” or “weakly” ferromagnetic mean in the collective electron theory of Stoner: the quantity α X o in the “enhancement factor” D = X / X o = (1 – α X 0 ) −1 is in the first case only a little smaller, in the second case only a little greater than one ( X 0 spin susceptibility without interaction, α molecular field coefficient). A theory developed for such cases by Wohlfarth and Edwards yields some simple expressions for the temperature or field dependence of the magnetization. The theory can be applied only on condition that the constituants of the alloy form a common d‐band (for example RhNi). But often that is not so. In such cases (e.g. RhCo), the transition from paramagnetism to ferromagnetism obviously occurs by augmentation of localized d‐states with or without magnetic moment. Some examples are described. In the system CuNi, the transition is prepared by the formation of superparamagnetic clusters at ≈32 atyo Ni; interaction of the clusters produces ferromagnetism at ≈44 atyo Ni (Kouvel and Comly).