Magnetocaloric effect, magnetostructural and magnetic phase transformations in Ni50.3Mn36.5Sn13.2 Heusler alloy ribbons

Abstract Thermomagnetic properties and magnetocaloric effect (MCE) in Ni 50.3 Mn 36.5 Sn 13.2 Heusler alloy ribbons are reported. Large magnetocaloric response has been obtained for μ 0 H  = 3 T in both the reversible adiabatic change in temperature Δ T ad (−6.3 and +4.7 K) and the isothermal change in the total entropy Δ S T (+11.8 and −2.2 J K −1  kg −1 ), respectively at the temperature T str  = 271 K at which the magnetostructural phase transition from the low-temperature Martensite phase (MP) to the high-temperature Austenite phase (AP) takes place, and at T CA  = 311 K at which the magnetic phase transition in the AP occurs. The MCE has been studied through the Stoner’s magnetocaloric parameter ξ S (Stoner EC. Phil Mag 19 (1935) 565), and a generalized expression for the equations of state for magnetic materials is presented. The phase coexistence of the MP and AP has been studied via their respective sublattice with opposite-aligned magnetic moments by means of the effective magnetic anisotropy density e A induced by the supercooled (superheated) secondary AP (MP) in the MP (AP). Magnetic fields higher than the critical value of μ 0 H R  = 0.5 T produce alignment of the two magnetic moments and hence a change in the magnetic ordering in the MP from antiferromagnetic to ferromagnetic, resulting in a thermomagnetic behavior in which the field-cooling and field-heating magnetizations become coincident, the induced anisotropy vanishes e A  = 0 and the metastability disappears. New tentative methods to obtain the spontaneous magnetization of both MP and AP and their respective fractions in the phase coexistence range are reported.