Magnetocaloric properties and exchange bias effect in Al for Sn substituted Ni_(48)Mn_(39.5)Sn_(12.5) Heusler alloy ribbons

摘要

The influence of Al substitution for Sn on magnetocaloric properties and exchange bias behavior in Ni_(48)Mn_(39.5)Sn_(12.5-x)Al_x (x=0, 1, 2, 3) melt spun ribbons have been investigated. All the studied ribbons undergo a martensitic and reverse transformation. At low temperature martensite region, below 100 K, the alloys exhibit exchange bias effect, which appears to enhance with the increase of Al concentration. The loop shift difference (△H_E) of up to 7960 A m~(-1) is recorded between the ribbon containing no Al and the ribbon with x=3. The presence of exchange bias behavior in these samples is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions. The magnetic entropy change and refrigerant capacity are evaluated for the ribbons studied around both the structural and magnetic transformations under the applied magnetic field induction of 2 T. The maximum entropy change around the magnetic transition and around the structural transition is reported for the Ni_(48)Mn_(39.5)Sn_(12.5) ribbon, and the entropy values amount to 1.8 and 7.8 J kg~(-1) K~(-1), respectively.