Magnetic critical phenomena and low temperature re-entrant spin-glass features of Al$_2$MnFe Heusler alloy

Abstract: A detailed investigation of the structural and magnetic properties, including magnetocaloric effect, re-entrant spin-glass behavior at low temperature, and critical behavior in polycrystalline Al$_2$MnFe Heusler alloy is reported. The prepared alloy crystallizes in a cubic CsCl-type crystal structure with Pm-3m space group. The temperature-dependent magnetization data reveals a second-order paramagnetic to ferromagnetic phase transition ($\sim$ 122.9 K), which is further supported by the analysis of the magnetocaloric effect. The isothermal magnetization loops show a soft ferromagnetic behavior of the studied alloy and also reveal an itinerant character of the underlying exchange interactions. In order to understand the nature of magnetic interactions, the critical exponents for spontaneous magnetization, initial magnetic susceptibility, and critical MH isotherm are determined using Modified Arrott plots, Kouvel-Fisher plots, and critical isotherm analysis. The derived critical exponents $\beta$ = 0.363(2), $\gamma$ = 1.384(3), and $\delta$ = 4.81(3) confirm the critical behavior similar to that of a 3D-Heisenberg-type ferromagnet with short-range exchange interactions that are found to decay with distance as J(r) $\approx$ r$^{-4.936}$. Moreover, the detailed analysis of the AC susceptibility data suggests that the frequency-dependent shifting of the peak temperatures is well explained using standard dynamic scaling laws such as the critical slowing down model and Vogel-Fulcher law, and confirms the signature of re-entrant spin-glass features in Al$_2$MnFe Heusler alloy. Furthermore, maximum magnetic entropy change of $\sim$ 1.92 J/kg-K and relative cooling power of $\sim$ 496 J/kg at 50 kOe applied magnetic field are determined from magnetocaloric studies that are comparable to those of other Mn-Fe-Al systems.