Metamagnetic transition and susceptibility maximum in an itinerant-electron system

Abstract

An itinerant-electron metamagnetism is discussed at finite temperature, by taking into account the effect of spin fluctuations on the Landau-Ginzburg theory. It is shown that the paramagnetic susceptibility always shows a maximum in its temperature dependence when the metamagnetic transition from the paramagnetic to the ferromagnetic state is induced by the external magnetic field at low temperature. This metamagnetic transition, associated with a hysteresis in the magnetization curve, is shown to disappear at high temperature. Moreover, the first-order transition in the temperature dependence of the spontaneous magnetization is shown to occur under a certain condition among the Landau coefficients. Three characteristic temperatures, at which the susceptibility reaches a maximum, the field-induced metamagnetic transition disappears, and the temperature-induced first-order transition of the magnetization occurs, are discussed. The present theory can explain qualitatively these anomalous magnetic properties observed in Co compounds Co(S,Se${)}_2$, ${\mathrm{YCo}}_2$, ${\mathrm{LuCo}}_2$, and others.