Exotic magnetic behaviour and evidence of cluster glass and Griffiths like phase in Heusler alloys Fe _2-xMn _xCrAl (0 ≤ x ≤ 1)

Abstract

We present a detailed study of structural, magnetic and thermodynamic properties of a series of Heusler alloys Fe _2-xMn _xCrAl (x = 0, 0.25, 0.5, 0.75 and 1). Structural investigation of this series is carried out using high resolution synchrotron X-ray diffraction. Results suggest that with increasing Mn concentration, the L2 ₁ structure of Fe ₂CrAl is destabilized. The DC magnetization results show a decrement in paramagnetic (PM) to ferromagnetic (FM) phase transition temperature ( T _C) with increasing Mn concentration. From the systematic analysis of magnetic memory effect, heat capacity, time dependent magnetization, and DC field dependent AC susceptibility studies it is observed that, Fe ₂CrAl exhibits cluster glass(CG)-like transition approximately at 3.9 K ( T _f2). The alloys, Fe _1.75Mn _0.25CrAl and Fe _1.5Mn _0.5CrAl exhibit double CG-like transitions near T _f1 ~ 22 K, T _f2 ~ 4.2 K and T _f1 ~ 30.4 K, T _f2 ~ 9.5 K respectively, however, in Fe _1.25Mn _0.75CrAl, a single CG-like transition is noted at T _f2 ~ 11.5 K below T _C. Interestingly, FeMnCrAl shows the absence of long ranged magnetic ordering and this alloy undergoes three CG-like transitions at ~22 K ( T _f ^*), 16.6 K ( T _f1) and 11 K ( T _f2). At high temperatures, a detailed analysis of temperature response of inverse DC susceptibility clearly reveals the observation of Griffiths phase (GP) above 300 K ( T*) in Fe ₂CrAl and this phase persists with Mn concentration with a decrement in T*.