P-T-B magnetic phase diagram of itinerant-electron metamagnets

Temperature and pressure dependencies of a metamagnetic transition (MT) in an isotropic itinerant-electron system are discussed in terms of a spin fluctuation model based on the Ginzburg-Landau theory, including magnetoelastic energy. It has been shown that the critical magnetic field BC of the MT increases as temperature T and pressure P increase. Both first- and second-order transitions of the magnetization at the Curie temperature TC are derived, depending on the characteristic quantity q(0) of the MT given by Landau parameters. It has been obtained that the TC of the first-order transition is proportional to (PC-P)1/2 near the critical pressure PC, as has been observed in MnSi and La(Fe,Si)13. By the numerical calculations, a three-dimensional (P, T, B) magnetic phase diagram is obtained.