Role of Spin Fluctuation in Spontaneous Magneto-Volume Effects of Intermetallic Compounds MnAs and MnAs_1−xP_x

Abstract

The magneto-volume effects of intermetallic compounds MnAs and MnAs_1−xP_x are studied from the viewpoint of itinerant electrons. Using the free energy obtained by the spin fluctuation theory we calculate the pressure as a function of temperature, from which the spontaneous volume magnetostriction is obtained. We have made calculations for the paramagnetic and ferromagnetic states of the NiAs-type structure and for the paramagnetic state of the MnP-type structure. The observed anomalous temperature dependence of the volume in the intermediate phase of the MnP-type structure and a discontinuous volume change at the Curie temperature are well explained by the effects of spin fluctuations.