Prediction of the Magnetocaloric Effect of the Ni₄₃Mn₄₅CoSn₁₁ Heusler Alloy with a Phenomenological Model

Intermetallic NiMn-based Heusler alloys (HAs) have attracted great consideration owing to their multi-functionality and exploration in various fields covering sensors, actuation, refrigeration, and waste heat harvesters. Among the NiMn-based HAs, Ni-Mn-Sn alloys have gained much attention since the structural and magnetic transformation was discovered. Many studies have been conducted with different compositions and shapes to explore the physical properties of Ni-Mn-Sn HAs as they present many advantages, such as being non-toxic, low-cost, and having abundant constituents. The Co-doping effect on the physical properties of Ni-Mn-Sn alloys has been widely reported. This doping can rectify the ternary Ni-Mn-Sn Heusler compound's brittleness by crystallizing a disordered face-centered cubic (fcc) γ-phase.

In this study, a polycrystalline Ni₄₃Mn₄₅CoSn₁₁ Heusler alloy was prepared by high-frequency fusion (HF), using a Lin Therm 600 device, from pure Ni, Mn, Sn, and Co elements with appropriate proportions. X−ray diffractometer (BRUCKER D8 Discover), scanning electron microscope (FEI Quantum 250), and magnetometer BS1 devices were used to study the structural, microstructural, and magnetic properties.

The XRD results revealed the coexistence of an ordered L2₁ cubic-austenite phase (~88%) and a disordered cubic solid solution γ-phase (~12%). The alloy undergoes a second-order ferromagnetic to paramagnetic phase transition at a Curie temperature of Tc = 350 K. Landau and Hamad's theoretical models have been used to re-plot the magnetic entropy change. The magnetocaloric properties (the maximum entropy change value, ΔS_M, the full width at half maximum of the entropy change curve, δT_FWHM, the relative cooling power, RCP, and the heat capacity, ΔC_P,H ) have been calculated using the isothermal magnetization curves with the phenomenological model of Hamad.