Magnetically ordered materials: relation between internal energy, magnetization and applied field

Grout and March [Phys. Rev. B 14 (1976) 4027] emphasized a relation between internal energy E and magnetization M at low temperatures, noting in particular the difference between insulating and metallic ferromagnets. Independently Milotti [Phys. Rev. E 63 (2001) 026116] has used the Ising model, but with the admittedly simplistic assumption of infinite-range interaction, to discuss both magnetization and specific heat, including an applied magnetic field. It is argued here that Milotti's results have a bearing on transition metals exhibiting long-range magnetic order, exchange interactions in the materials having larger ranges than in insulating counterparts. Some features of the theoretical predictions are shown to be reflected in properties of the ferromagnetic metals Fe, Ni and Co and also in the antiferromagnetic metal Mn. (C) 2004 Elsevier B.V. All rights reserved.