Magnetocaloric properties and critical behavior of Co2Cr1−xMnxAl Heusler alloys

• Published in: Journal of applied physics 2019-11, Vol.126 (20)
• Main Authors: Nehla, Priyanka, Anand, V. K., Klemke, Bastian, Lake, Bella, Dhaka, R. S.
• Format: Article
• Language: English
• Subjects: Applied physics; Collapse; Curie temperature; Decay rate; Diffraction patterns; Entropy; Ferromagnetism; Heusler alloys; Isotherms; Magnetic moments; Magnetic permeability; Magnetic properties; Magnetism; Manganese; Mean field theory; Phase transitions; Refrigerators; Temperature dependence; Transition temperature
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.5128157

We study the magnetocaloric effect and critical behavior of Co 2 Cr 1 − x Mn x Al ( x = 0.25, 0.5, 0.75) Heusler alloys across the ferromagnetic (FM) transition temperature ( T C). The Rietveld refinement of x-ray diffraction patterns exhibit a single phase cubic structure for all the samples. The temperature dependent magnetic susceptibility χ ( T ) data show a systematic enhancement in the Curie temperature and effective magnetic moment with the Mn concentration, which is consistent with the Slater–Pauling behavior. The M ( H ) isotherms also exhibit the FM ordering, and the analysis of χ ( T ) data indicates the nature of the phase transition to be a second order, which is further supported by scaling of the entropy curves and the Arrott plot. Interestingly, the Mn substitution causes an increase in the magnetic entropy change and, hence, a large relative cooling power for possible applications in multistage magnetic refrigerators. In order to understand the nature of the magnetic phase transition, we examine the critical exponents β, γ, δ for the x = 0.75 sample by the modified Arrott plot and the critical isotherm analysis, which is further confirmed by the Kouvel-Fisher method and Widom scaling relation, respectively. The estimated values of β = 0.507, γ = 1.056, δ = 3.084 are found to be close to the mean field theoretical values. The renormalized isotherms (m vs h) corresponding to these exponent values collapse into two branches, above and below T C that validates our analysis. Our results suggest the existence of long-range FM interactions, which decays slower than power law as J ( r ) ∼ r − 4.5 for a three-dimensional mean-field theory.