Magneto-volume effects in weakly ferromagnetic metals

Magneto-volume effects of weakly ferromagnetic metals are discussed, based on the assumption that the local spin fluctuation amplitude is almost constant. The author's result on the thermal expansion agrees with the result of Moriya and Usami (1980). He derives the universal relation of the ratio of thermal expansion above the Curie temperature and the spontaneous magnetostriction. Based on a simple thermodynamic argument, he also derives a relation connecting the magneto-volume coupling coefficient with the pressure dependence of the Curie temperature, which is slightly different from the Stoner-Wohlfarth theory.