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

Abstract

The Curie temperature TC of La(Fe0.89Si0.11)13 in inhomogeneous and homogeneous (single phase) states is controlled by heat treatment and hydrogen absorption. The magnetization change at TC around room temperature of the inhomogeneous specimens composed of α-Fe, LaFeSi, and La(FexSi1-x)13 phases becomes sluggish after hydrogen absorption, because TC 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 ΔSm due to the itinerant-electron metamagnetic transition of these specimens is decreased by hydrogen absorption. On the other hand, the magnitude of ΔSm after hydrogen absorption into the single-phase specimen is almost the same as that before hydrogen absorption. Consequently, the compositional homogenization in La(FexSi1-x)13 is necessary to obtain large magnetocaloric effects around room temperature.