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

摘要

The influence of a partial substitution of Ce or Pr on the magnetocaloric effects due to the itinerant electron metamagnetic transition of $hbox{La}{(hbox{Fe}_{rm x}hbox{Si}_{1-{rm x}})}_{13}$ has been investigated. The partial substitution of $hbox{R}=hbox{Ce}$ or Pr for La in $hbox{La}_{1-{rm z}}hbox{R}_{rm z}{(hbox{Fe}_{0.88}hbox{Si}_{0.12})}_{13}$ results in the decrease of the Curie temperature $T_{rm C}$ with decreasing the lattice constant. For the partial substitution of Ce, the change in $T_{rm C}$ is mainly attributed to the magnetovolume effect caused by small radius of Ce atoms. The influence of Pr moment on $T_{rm C}$ is also pointed out. The increase of the isothermal entropy change $Delta S_{rm m}$ with decreasing $T_{rm C}$ is confirmed by both the partial substitution and application of hydrostatic pressure, although the increment of $Delta S_{rm m}$ by the latter is smaller than that by the former. The spin-wave dispersion coefficient $D_{rm sw}$ is slightly increased after partial substitutions in contrast to the application of hydrostatic pressure, and the reduction of thermal demagnetization up to $T_{rm C}$ brings about the enhancement of $Delta -n-nS_{rm m}$ . Accordingly, the increase in ferromagnetic stability due to the change in 3d band structure enhances $Delta S_{rm m}$, in addition to the magnetovolume effect. The hysteretic behavior of the IEM transition is reduced by decreasing Fe concentration, whereas $Delta S_{rm m}$ is enhanced by the partial substitution. Consequently, a marked reduction of hysteresis loss with retaining the large magnitude of $Delta S_{rm m}$ is demonstrated in $hbox{La}_{1-{rm z}}hbox{R}_{rm z}{(hbox{Fe}_{0.86}hbox{Si}_{0.14})}_{13}$ ($hbox{R}=hbox{Ce}$ and Pr). We have also presented that $T_{rm C}$ 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.