Magnetocaloric properties of as-quenched Ni50.4Mn34.9In14.7 ferromagnetic shape memory alloy ribbons

The temperature dependences of magnetic entropy change and refrigerant capacity have been calculated for a maximum field change of Δ H=30 kOe in as-quenched ribbons of the ferromagnetic shape memory alloy Ni_50.4Mn_34.9In_14.7 around the structural reverse martensitic transformation and magnetic transition of austenite. The ribbons crystallize into a single-phase austenite with the L2₁-type crystal structure and Curie point of 284 K. At 262 K austenite starts its transformation into a 10-layered structurally modulated monoclinic martensite. The first- and second-order character of the structural and magnetic transitions was confirmed by the Arrott plot method. Despite the superior absolute value of the maximum magnetic entropy change obtained in the temperature interval where the reverse martensitic transformation occurs (|\varDelta S_M^max|=7.2 J kg^-1 K^-1)(|\varDelta S_{\mathrm{M}}^{\max}|=7.2\mbox{ J}\,\mbox{kg}^{-1}\,\mbox{K}^{-1}) with respect to that obtained around the ferromagnetic transition of austenite (|\varDelta S_M^max|=2.6 J kg^-1 K^-1)(|\varDelta S_{\mathrm{M}}^{\max}|=2.6\mbox{ J}\,\mbox{kg}^{-1}\,\mbox{K}^{-1}), the large average hysteretic losses due to the effect of the magnetic field on the phase transformation as well as the narrow thermal dependence of the magnetic entropy change make the temperature interval around the ferromagnetic transition of austenite of a higher effective refrigerant capacity (RC^magn_eff=95J kg^-1\mathrm{RC}^{\mathrm{magn}}_{\mathrm{eff}}=95\mbox{J}\,\mbox{kg}^{-1} versus RC^struct_eff=60J kg^-1)\mathrm{RC}^{\mathrm{struct}}_{\mathrm{eff}}=60\mbox{J}\,\mbox{kg}^{-1}).