Structural, magnetic and magnetocaloric effect studies of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 Heusler alloys

Itegbeyogene P Ezekiel,Thomas Moyo

doi:10.1063/1.5037756

Abstract

We investigated the structural and magnetic properties of Ni42.5(Fe, Co, Ni, Cu)0.5Mn46Sn11 alloys fabricated by arc melting. Substitution of Ni by Fe, Co and Cu causes lattice expansions consistent with increasing atomic sizes. The zero-field cooled and field cooled results show second-order magnetic transition at the high-temperature austenite phase to a first-order magnetic transition in the low-temperature martensite phase. The substitution of Ni by Fe and Co increases the austenite Curie temperature TCA from 282 K to 289 K and 294 K respectively while Cu reduces it to 278 K. The martensitic transition temperature TM increased from 221 K to 241 K for Fe substitution and decreased to 210 K and 209 K for Co and Cu respectively. The coercive field HC increased significantly from 457 Oe for Ni at 100 K to 729 Oe for Co at 80 K. The increase to 763 Oe for Fe and 769 Oe for Cu occurred at the same temperature of 40 K. We attribute such increases to domain wall pinning effects due to the inclusions of Fe, Co and Cu. The HC exhibited an anomalous temperature dependence in all the samples. The exchange bias field HEX also showed a significant enhancement below 40 K from 196 Oe for Ni to 476 Oe, 430 Oe and 434 Oe for Fe, Co, and Cu substitutions respectively. The fits to the temperature dependence of the HC reveal significant changes in the competition between ferromagnetic and antiferromagnetic interactions. The peak magnetic entropy change ΔSMpk has a linear dependence on the magnetic field H2/3. The highest value of 28.8 J kg-1 K−1 for ΔSM is obtained in the first order magnetic transition compared to 3.0 J kg-1 K−1 in the second order transition. We report an effective cooling power of 155 J kg-1 in the second order magnetic transition.

Highlights

The metamagnetic behavior of these alloys produces large magnetic entropy change, ∆SM which is one of the primary parameters required to quantify the magnetocaloric effect (MCE) of magnetic materials used in solid-state refrigeration
We have presented a study of the influence of the Ni substitution by Fe, Co, and Cu on the structure, magnetic properties and the magnetocaloric effect
The coercivity and the exchange bias field significantly increased at temperatures below 100 K when Fe, Co, and Cu substitute Ni due to inclusions of Fe, Co and Cu atoms

Summary

Introduction

Magnetic materials that exhibit high magnetocaloric effect (MCE) have a high potential to replace conventional refrigerant materials that are not environmentally friendly.[1,2,3,4] Among the magnetic materials in focus are the off-stoichiometric Ni-Mn-X based Heusler alloys, where X can be Ga, Sn, In and Sb.[2,3,5,6] The metamagnetic behavior of these alloys produces large magnetic entropy change, ∆SM which is one of the primary parameters required to quantify the MCE of magnetic materials used in solid-state refrigeration. Off-stoichiometry Ni-Mn-X based Heusler alloys possess a low symmetry tetragonal or orthorhombic phase at low temperature referred to as the martensite phase and a high symmetry cubic phase at higher temperature known as the austenite phase.[7,8] The temperature dependent magnetization in Ni-Mn-X alloys show second-order magnetic transition around the region of the austenite phase and first-order magnetic transition to the martensite phase.[7,8,9] A large ∆SM is usually obtained at a temperature near the first order magnetic transition known as the martensitic

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Results

Conclusion