Magnetic and magnetocaloric properties of La(Fe,Co)11.4SP1.6 compounds (SP=Al or Si)

The influence of Co substitution on the structural and magnetic properties of La(Fe1−xCox)11.4SP1.6 compounds (SP=Al or Si) was investigated by X-ray diffraction, Mössbauer spectroscopy and magnetization measurements. The studied compounds were crystallized in the NaZn13 structure, with a fraction of α-Fe(Co,SP) phase. Partial substitution of Fe by Co atoms changes (i) the magnetic ordering temperature (200 K0.04x>0.04, the compounds are ferromagnetic as the ground state. On the other hand, the Si compounds have ferromagnetic ground state for all Co compositions studied. The field-induced (5 T) maximum magnetic entropy variation remains almost constant at about −5 J/kg K, for x values up to 0.12, in the Al compound. However, this entropy variation reduces from −18 to −5 J/kg K (∼72%), when Co substitution is increased from 0 to 8 at%. in the Si compounds. This effect may be associated with the disappearing of the first-order transition with the addition of Co. Metamagnetic transition of the Co free Al compound has entropy variation of 13 J/kg K at about 11 K.