Control of Magnetocaloric Effects by Partial Substitution in Itinerant-Electron Metamagnetic $\hbox{La}{(\hbox{Fe}_{\rm x}\hbox{Si}_{1-{\rm x}})}_{13}$ 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 DeltaS _m with decreasing T _C is confirmed by both the partial substitution and application of hydrostatic pressure, although the increment of DeltaS _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 DeltaS _m . Accordingly, the increase in ferromagnetic stability due to the change in 3d band structure enhances DeltaS _m, in addition to the magnetovolume effect. The hysteretic behavior of the IEM transition is reduced by decreasing Fe concentration, whereas DeltaS _m is enhanced by the partial substitution. Consequently, a marked reduction of hysteresis loss with retaining the large magnitude of DeltaS _m is demonstrated in La_1-zR_z(Fe_0.86Si_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.