XLIII. Collective electron ferromagnetism: Rectangular energy bands.

Abstract

Calculations similar to those of Stoner (1938, 1939) are carried out for an energy band for which the energy density of states is constant. These have a bearing on calculations of the actual band form for nickel (Fletcher and Wohlfarth 1951). After brief reference to previous work and a statement of the basic assumptions of the treatment, relations are derived giving the dependence on temperature and the interchange interaction energy of the spontaneous magnetization below and the susceptibility above the Curie point. Various explicit limiting relations are deduced. The numerical results of the calculations are given in Table I. and fig. 1 (§2). Formulae are also derived which give the internal energy and specific heat over the whole temperature range. Relations are given for the most important experimentally observable thermal characteristics, such as the specific heat discontinuity at the Curie point. The results are shown in figs. 2 and 3 (§3). Experimental results which are briefly discussed (§4) include those on the magnetic properties of nickel and its alloys and the thermal properties of nickel, including the energy and specific heat characteristics, the temperature variation of specific heat and the magneto-caloric effect. The high temperature specific heat of paramagnetics is also discussed. In an Appendix certain results for an energy band of more general form are given.