Control of magnetocaloric effects by partial substitution in itinerant-electron metamagnetic La(Fe_xSi_1-x)₁₃ for application to magnetic refrigeration

The influence of a partial substitution of Ce or Pr on the magnetocaloric effects due to the itinerant electron metamagnetic transition of La(Fe _xSi_1-x)₁₃ has been investigated. The partial substitution of R = Ce or Pr for La in La_1-zR_z(Fe _0.88Si_0.12)₁₃ results in the decrease of the Curie temperature T_c with decreasing the lattice constant. For the partial substitution of Ce, the change in T_C is mainly attributed to the magnetovolume effect caused by small radius of Ce atoms. The influence of Pr moment on T_C is also pointed out. The increase of the isothermal entropy change δS_m with decreasing T_C is confirmed by both the partial substitution and application of hydrostatic pressure, although the increment of δS_m by the latter is smaller than that by the former. The spin-wave dispersion coefficient D_sw is slightly increased after partial substitutions in contrast to the application of hydrostatic pressure, and the reduction of thermal demagnetization up to T _C brings about the enhancement of δS_m. Accordingly, the increase in ferromagnetic stability due to the change in 3d band structure enhances δS_m, in addition to the magnetovolume effect. The hysteretic behavior of the IEM transition is reduced by decreasing Fe concentration, whereas δS_m is enhanced by the partial substitution. Consequently, a marked reduction of hysteresis loss with retaining the large magnitude of δ S_m is demonstrated in La _1-zR_z(Fe_0.96Si_0.14)₁₃ (R = Ce and Pr). We have also presented that T_C in the partially substituted compounds with Ce or Pr is increased up above room temperature by hydrogen absorption, keeping the enhancement of MCEs by the partial substitution.