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
_0.89
Si
_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(Fe
x
Si
_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 Δ
S
_m
due to the itinerant-electron metamagnetic transition of these specimens is decreased by hydrogen absorption. On the other hand, the magnitude of Δ
S
_m
after hydrogen absorption into the single-phase specimen is almost the same as that before hydrogen absorption. Consequently, the compositional homogenization in La(Fe
x
Si
_1-
x
)
₁₃
is necessary to obtain large magnetocaloric effects around room temperature.