Effect of the magnetic prehistory on the low-temperature heat capacity of the La(Fe0.88Al0.12-xSix)13 compounds

The measured heat capacity C of solids is thought in general to involve the change of the internal energy which is a state property. Therefore the electron density of states at the Fermi level is derived from the low-temperature data C=gamma T + beta T-3. The La(Fe0.88Al0.12-xSix)(13) compounds are the antiferromagnets (AFM) T-N=200 K with 0<x<0.03 and the ferromagnets (FM) with 0.03<x<0.12 T-C=194 K. For x=0.024 and x=0.027 a metamagnetic phase transition from AFM to the field-induced FM (FIFM) occurs in low external magnetic field. The FIFM state of the sample remains if the magnetic field turns off. The measurements of the low-temperature heat capacity in this FIFM state have shown an increase of coefficient gamma in comparison with the value both the AFM and the FM. The measured heat capacity depends on a thermodynamic path and thus is not a state property. The change of the work of the magnetostrictive strain of the sample as a part of the low-temperature heat capacity is discussed.