Magnetic properties and magnetocaloric effect in Nd_xLa_1-xFe_11.5Al_1.5 compounds

Effects of Nd-doping on the magnetic properties and magnetocaloric effects (MCEs) of Nd_xLa_1 - xFe_11.5Al_1.5 have been investigated. Substitution of Nd leads to a weakening of the antiferromagnetic (AFM) coupling and an enhancement of the ferromagnetic (FM) coupling. This in turn results in a complex magnetic behaviour for Nd_0.2La_0.8Fe_11.5Al_1.5 characterized by the occurrence of two phase transitions at \sim188 K (PM--AFM) and \sim 159 K (AFM--FM). As a result, a table-like MCE (9 J/kg\cdotK) is found in a wide temperature range (160--185 K) for a field change of 0--5 T around the transition temperature, as evidenced by both the magnetic and calorimetric measurements. Based on the analysis of low-temperature heat capacity, it is found that the AFM--FM phase transition modifies the electron density significantly, and the major contribution to the entropy change comes from the electronic entropy change.