Unconventional critical behaviour in weak ferromagnets Fe_2-xMn_xCrAl (0 ≤ x < 1)

Recent investigation on weak ferromagnets Fe_2-xMn_xCrAl (0 ≤ x < 1) reveal the existence of a cluster glass phase (CGP) and a Griffiths-like phase (GP) below and above the ferromagnetic transition temperature (T_C), respectively [(2019) Sci. Rep. 9 15888]. In this work, the influence of these inhomogeneous phases on the critical behaviour (around T_C) of the above-mentioned series of alloys has been investigated in detail. For the parent alloy Fe₂CrAl, the critical exponent γ is estimated as ~ 1.34, which lies near to the ordered 3D Heisenberg class, whereas the obtained value of the critical exponent β ~ 0.273 does not belong to any universality class. With increment in Mn concentration, both exponents γ and β increase, where γ and β approach the disordered and ordered 3D Heisenberg class, respectively. The observed deviation of γ and unconventional value of δ can be ascribed to the increment of GP with Mn-concentration. The trend noted for β can be attributed to the increment in CGP regime with an increase in Mn-content. The estimated critical exponents are consistent and reliable as corroborated using the scaling law and equations of state. Our studies indicate that the critical phenomenon of Fe_2-xMn_xCrAl (0 ≤ x < 1) alloys possibly belong to a separate class, which is not described within the framework of any existing universal model.