Effect of R substitution on magnetic properties and magnetocaloric effects of La_1-xR_xFe_11.5Si_1.5 compounds with R=Ce, Pr and Nd

Magnetic properties and magnetocaloric effects of La_1 - xR_xFe_11.5Si_1.5 (R=Pr, (0 \le x \le 0.5); R = Ce and Nd, (0 \le x \le 0.3)) compounds are investigated. Partially replacing La with R = Ce, Pr and Nd in La_1 - xR_xFe_11.5Si_1.5 leads to a reduction in Curie temperature due to the lattice contraction. The substitution of R for La causes an enhancement in field-induced itinerant electron metamagnetic transition, which leads to a remarkable increase in magnetic entropy change \Delta S_\rm m and also in hysteresis loss. However, a high effective refrigerant capacity RC_\rm eff is still maintained in La_1 - xR_xFe_11.5Si_1.5. In the present samples, a large \Delta S_\rm m and a high RC_\rm eff have been achieved simultaneously.