Hydrogenation and magnetocaloric effect in La-excessive La Fe11.5Si1.5 H alloys

Abstract In this study, we report on the kinetics of hydrogen absorption in LaxFe11.5 Si1.5 alloys with x = 1.0, 1.1, 1.2, and 1.3 as well as the magnetocaloric properties in the corresponding hydrides. Hydrogen absorption experiments reveal that both hydrogen pressure and reaction temperature considerably affect the kinetics of hydrogen absorption and the hydrogen content absorbed in the alloys. The studied alloys exhibit excellent kinetics of hydrogen absorption when the reaction temperature is in the range of 483–543 K under a final balanced hydrogen pressure of no less than 0.02 MPa. The Curie temperature is significantly improved close to room temperature through hydrogenation in the studied alloys. For a field change of 3 T, the hydrogenated alloys present absolute values of maximum isothermal entropy changes of 13.4, 17.2, 17.9, and 17.3 J/kg ⋅ K for x = 1.0, 1.1, 1.2, and 1.3, respectively. The isothermal entropy changes of the La-excessive hydrides are approximately 30% higher than that of the hydride with x = 1.0. The results suggest that La-excessive hydrides are promising refrigerants for magnetic refrigeration near room temperature.