Critical behavior and magnetocaloric effect in Co50−xNixCr25Al25 (x = 0 and 5) full Heusler alloy system

Abstract

This work reports the investigation of critical behavior of Co50−xNixCr25Al25 (x=0 and 5) and magneto caloric effect (MCE) of bulk Co2CrAl full Heusler alloy system. The alloy series of Co50−xNixCr25Al25 (x=0, 1, 2, 3, 4 and 5) have been prepared using arc melting technique. The magnetic properties of all the samples have been studied in the temperature range of 5–300K. The value of Curie temperature (TC) is found to decrease with increasing doping concentration of the Ni (substitution of Ni at Co site). The critical exponents behavior and scaling relation have been investigated using magnetic isotherms in Co50−xNixCr25Al25 (x=0 and 5) alloys. The critical exponents are estimated by various techniques such as, Modified Arrott plot, Kouvel–Fisher plot and critical isotherm technique. The value of critical exponents vicinity to the second order magnetic phase transition of Co50Cr25Al25 were found to be β=0.488 (7), γ=1.144 (16) and δ=3.336 (5) with TC=328.64 (5)K whereas for Co50Ni5Cr25Al25 the values are β=0.522 (13), γ=1.014 (6) and δ=3.043 (7) with TC=285.71 (11). The critical exponent values for both the samples are almost similar to the value as predicted by mean field theory. This has been best explained by long range mean field like ferromagnetic interaction in the entire Co50−xNixCr25Al25 (x=0, 5) highly spin polarized full Heusler alloy system. Under an external magnetic field maximum up to 5T, normal magneto caloric effect (MCE) have been observed with a maximum magnetic entropy change of 2.55J/kgK at 328.5K (near the ferromagnetic→paramagnetic second order magnetic phase transition in the austenite phase) in Co2CrAl full Heusler alloy system.