High-Temperature Thermomagnetic and Magnetic Properties of CoMnAl Half-Heusler Alloy

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Abstract
Polycrystalline CoMnAl alloy was synthesised by vacuum arc melting followed by annealing to investigate its structural, magnetic, and magnetocaloric properties. PowderX-ray diffraction combined with Rietveld refinement, using the NiMnSb-type half-Heusler structural model, confirmed the formation of a single-phase cubic structure with space group 𝐹 ̄43𝑚 (No. 216). The refined lattice parameter was determined to be 𝑎 = 5.789(3) Å, with good agreement between the experimental and calculated diffraction profiles. Room-temperature magnetic measurements revealed soft ferromagnetic behaviour, with a saturation magnetisation of approximately 118 Am2 kg-1, a low coercive field of 8.6 Oe, and an effective magnetic anisotropy constant of 28.5 kJm-3. Temperature-dependent magnetisation measurements revealed a continuous ferromagnetic–paramagnetic transition at a Curie temperature of approximately 624 K. The temperature dependence of the magnetisation was further analysed using the modified Bloch model, from which the spin-wave stiffness constant was estimated.