Concentration Dependence of Pressure Effect in La(Fe<I><SUB>x</SUB></I>Si<SUB>1−<I>x</I></SUB>)<SUB>13</SUB> Compounds

Abstract

Effects of pressure P on the magnetic moment M and the Curie temperature T C have been investigated for La(Fe x Si 1-x ) 13 above and below the magnetic phase boundary concentration x = 0.86, where the ferromagnetic-paramagnetic transition at T C changes from the first-order (x ≥ 0.86) to the second-order (x < 0.86). The pressure coefficient ofM exhibits a sluggish variation against concentration and no anomaly was observed at x = 0.86, being consistent with the Landau expansion model. On the other hand, T C for the second-order transition has a large negative pressure coefficient dT C /dP and its magnitude increases with increasing x. Above x = 0.86, the magnitude of dT C /dP for the first-order transition increases with x, contrary to the theoretical expectation. It has been revealed that the spin-wave dispersion coefficient becomes smaller when the first-order transition becomes clear by changing the concentration and also applying pressure. Consequently, it is plausible that dTc/dP above x = 0.86 is enhanced by the increase of instability of the ferromagnetic state.