Ehrenfest Relations and Magnetoelastic Effects in Field-induced Ordered Phases

Abstract

Magnetoelastic properties in field-induced magnetic ordered phases are studied theoretically based on a Ginzburg–Landau theory. A critical field for the field-induced ordered phase is obtained as a function of temperature and pressure, which determine the phase diagram. It is found that magnetic field dependence of elastic constant decreases discontinuously at the critical field, H_c, and that it decreases linearly with field in the ordered phase (H>H_c). We found an Ehrenfest relation between the field dependence of the elastic constant and the pressure dependence of critical field. Our theory provides the theoretical form for magnetoelastic properties in field- and pressure-induced ordered phases.