Investigation of the critical behaviour and magnetocaloric effect in γ-Fe49Ni29Cr22 disordered austenitic stainless steel alloy by using the field dependence of magnetic entropy change

Abstract

We have reported here the critical behaviour and magnetocaloric effect (MCE) around the ferromagnetic (FM) → paramagnetic (PM) phase transition temperature (Tc) in a γ-Fe49Ni29Cr22 disordered austenitic stainless steel alloy system through detailed ac and dc magnetization study. The value of critical exponents have been estimated using the recorded M−H isotherms SQUID data using different techniques such as modified Arrott plots, Kouvel–Fisher plots, and critical isotherm analysis. The critical exponents values of γ-Fe49Ni29Cr22 alloy are found to be β = 0.440 (7), γ = 1.340 (16) and δ = 3.336 (5) with Tc = (124.82 ± 0.01) K. From the detailed DC magnetization study, the observed non-hysteretic M-T data in FCC and FCW mode, positive slope in the entire range of the Arrott plots near TC (Banerjee criterion), it confirms a second order FM → PM phase transition at TC. Though the nature of this transition is found to be of second order, the estimated critical exponent values β, γ, and δ are in between the theoretically predicted values for 3d Heisenberg and mean-field spin interaction models. However, it is important that these critical exponents obeyed the single scaling relations [M(H,ε)=|ε|βf±(H,|ε|−(β+γ))] indicating renormalization of interactions around the Curie temperature (TC). Temperature variation in effective critical exponents (βeff and γeff) resemble with those for various disordered ferromagnets as found in our γ-Fe49Ni29Cr22 alloy system. We have also estimated the normal MCE with maximum entropy change of 1.8 J/kg-K at 125.5 K under an external magnetic field change of 5 T in the austenite phase of the alloy.