Magnetocaloric properties and critical behavior of Co2Cr1 xMnxAl Heusler alloys

We study the magnetocaloric effect and critical behavior of Co2Cr1 xMnxAl x 0 25, 0.5, 0.75 Heusler alloys across the ferromagnetic FM transition temperature TC . The Rietveld refinement of x ray diffraction patterns exhibit a single phase cubic structure for all the samples. The temperature dependent magnetic susceptibility amp; 967; 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 amp; 967; 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 amp; 946;, amp; 947;, amp; 948; 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 amp; 946; 0 507, amp; 947; 1 056, amp; 948; 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 TC 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 theor