The itinerant-electron metamagnetic (IEM) transition and magnetocaloric effects (MCE’s) in the $\mathrm{La}({\mathrm{Fe}}_x{\mathrm{Si}}_{1-x}{)}_{13}$ and $\mathrm{La}({\mathrm{Fe}}_x{\mathrm{Si}}_{1-x}{)}_{13}{\mathrm{H}}_y$ compounds have been investigated. The $\mathrm{La}({\mathrm{Fe}}_x{\mathrm{Si}}_{1-x}{)}_{13}$ compounds exhibit large values of both the isothermal entropy change $\Delta S_{\mathrm{m}}$ and the adiabatic temperature change $\Delta T_{\mathrm{ad}}$ around the Curie temperature $T_{\mathrm{C}}$ in relatively low magnetic fields. Such large MCE’s are explained by a large magnetization change at $T_{\mathrm{C}}$ and a strong temperature dependence of the critical field $B_{\mathrm{C}}$ for the IEM transition. By hydrogen absorption into the compounds, $T_{\mathrm{C}}$ is increased up to about 330 K, keeping the metamagnetic transition properties. Accordingly, the extension of the working temperature range having the large MCE’s in relatively low magnetic fields is demonstrated by controlling y in the $\mathrm{La}({\mathrm{Fe}}_x{\mathrm{Si}}_{1-x}{)}_{13}{\mathrm{H}}_y$ compounds. The correlation between the increase of $T_{\mathrm{C}}$ and the large MCE’s in the $\mathrm{La}({\mathrm{Fe}}_x{\mathrm{Si}}_{1-x}{)}_{13}{\mathrm{H}}_y$ compounds is discussed by taking the magnetovolume effects into consideration.

• Received 1 October 2002

DOI:https://doi.org/10.1103/PhysRevB.67.104416