To elucidate the influence of hydrogenation on the volume dependence of the Curie temperature TC and the entropy change ΔSm in La(Fe0.86Si0.14)13, magnetic properties under hydrostatic pressure have been investigated. In the thermomagnetization curves of La(Fe0.86Si0.14)13H1.1, the first-order phase transition becomes clearer due to the decrease of volume, as observed before hydrogenation. By hydrogenation, the reduction of the pressure dependence of TC by about 20% is caused by the magnetovolume contribution to the free energy. Meanwhile, the maximum value of ΔS m is increased in magnitude from -9 to -18 J/kgK by applying pressure of 1 GPa. Accordingly, the decrease of volume is also effective to enhance ΔSm after hydrogenation.
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