Low temperature re-entrant spin-glass features and magnetic critical phenomena of ferromagnetic Al2MnFe Heusler alloy

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 Z<inf>2</inf>XY-type Al<inf>2</inf>MnFe Heusler alloy is reported. The prepared alloy crystallizes in a cubic CsCl-type crystal structure with Pm3̄m space group. The temperature-dependent magnetization data reveals a second-order paramagnetic to ferromagnetic phase transition (≈ 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 M(H) isotherm are determined using Modified Arrott plots, Kouvel-Fisher plots, and critical isotherm analysis. The derived critical exponents β = 0.363(2), γ = 1.384(3), and δ = 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)≈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 the Z<inf>2</inf>XY-type Al<inf>2</inf>MnFe Heusler alloy. Furthermore, maximum magnetic entropy change of 1.92 J/kg-K and relative cooling power of 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. Although the values are lesser than those of pure Gd and other rare-earth based magnetocaloric materials, the studied Z<inf>2</inf>XY-type Heusler alloy shows remarkable magnetocaloric properties that can be harnessed for cost-effective applications.