Influence of Homogenization of Microstructual Composition on Hydrogen Absorption into ${\rm La}{({\rm Fe}_{\rm x}{\rm Si}_{1-{\rm x}})}_{13}$ Magnetic Refrigerants

The Curie temperature T_C of La(Fe_0.89Si_0.11)₁₃ in inhomogeneous and homogeneous (single phase) states is controlled by heat treatment and hydrogen absorption. The magnetization change at T_C around room temperature of the inhomogeneous specimens composed of α-Fe, LaFeSi, and La(FexSi_1-x)₁₃ phases becomes sluggish after hydrogen absorption, because T_C in the specimens has a distribution accompanied by some inhomogeneity of the hydrogen content. As a result, the magnitude of the isothermal magnetic entropy change ΔS_m due to the itinerant-electron metamagnetic transition of these specimens is decreased by hydrogen absorption. On the other hand, the magnitude of ΔS_m after hydrogen absorption into the single-phase specimen is almost the same as that before hydrogen absorption. Consequently, the compositional homogenization in La(FexSi_1-x)₁₃ is necessary to obtain large magnetocaloric effects around room temperature.