Large magnetocaloric effects and Landau coefficients of itinerant electron metamagnetic La(Fe_xSi_1-x)₁₃ compounds

By fitting magnetization curves on the basis of the Landau expansion, the magnetocaloric effects in itinerant electron metamagnetic La(Fe _xSi_1-x)₁₃ compounds have been investigated. Temperature dependence of the magnetic entropy change ΔS_m is represented by thermal variation of the Gibbs energy calculated from the fitted Landau coefficients. A relation between the magnitude of ΔS_m and the fourth-order Landau coefficient at 0 K is described. It is also demonstrated that the energy barrier between the ferromagnetic and the paramagnetic states is easily overcome by thermal activation. Accordingly, the adiabatic process is slightly influenced by the energy barrier and the adiabatic temperature change comes close to an ideal value.