Difference in magnetic properties and magnetocaloric effect of FeRh0.98Al0.02 alloy with different sample sizes

Magnetic and magnetocaloric properties of the polycrystalline FeRh0.98Al0.02 alloy have been investigated as function of its physical state. A flake FeRh0.98Al0.02 sample undergoes an antiferromagnetic (AFM)-ferromagnetic (FM) phase transition around 275 K during heating and displays a 20 K thermal hysteresis upon the following cooling with an applied field of 5kOe. However, for a solid chunk sample, the transition temperature is around 308 K on heating and the hysteresis is 16 K. The maximum magnetic entropy change (ΔSM ) is 3.1 and 2.7 J/kg K for μ 0ΔH = 30 kOe and the refrigerant capacity (RC) is 120 and 185 J/kg for the flake and chunk samples, respectively. The temperature of the ΔSM maximum for the flake samples changes for different values of ΔH, which is characteristic for a first-order transition. On the other hand, the temperature remains almost constant for the chunk sample.