Coexistence of conventional and inverse magnetocaloric effects and critical behaviors in Ni50Mn50−<i>x</i>Sn<i>x</i> (<i>x</i> = 13 and 14) alloy ribbon<b>s</b>

Abstract

A systematic study of the conventional and inverse magnetocaloric effects and critical behaviors in Ni50Mn50−xSnx (x = 13 and 14) alloy ribbons has been performed. We show that although the magnetic entropy change around the second-order ferromagnetic-paramagnetic (FM-PM) transition (ΔSm ≈ −4 J/kg K) in the austenitic phase is about five times smaller than that around the first-order martensitic-austenitic (M-A) transformation (ΔSm ≈ 22 J/kg K), the refrigerant capacity (RC) – an important figure of merit – is about two times larger for the former case (RC ≈ 160 J/kg) than for the latter case (RC ≈ 75 J/kg). This finding points to an important fact that to assess the usefulness of a magnetocaloric material, one should not only consider ΔSm but also must evaluate both ΔSm and RC. Our critical analysis near the second-order FM-PM transition reveals that Sn addition tends to drive the system, in the austenitic FM phase, from the short-range (x = 13) to long-range (x = 14) FM order.