Enhanced magnetocaloric effect in melt-spun Mn[formula omitted]Fe[formula omitted]Ge3 (x = 0 and 1) ribbons with anisotropy induced spin-dimensionality crossover

Abstract

We report the structural, magnetic, magnetocaloric and ferromagnetic resonance properties of melt-spun Mn5−xFexGe3 (x = 0 and 1) ribbons. The melt-spun Mn5Ge3 ribbons exhibit hexagonal structure with preferential growth along c-axis while Fe doping retains the structure but changes preferential growth in in-plane direction. Fe doping enhances the ferromagnetic to paramagnetic phase transition temperature of Mn5Ge3 ribbons. Elaborate isothermal magnetization data analyses in the critical region yield critical exponents β= 0.344(1), γ= 1.284(1) and δ= 4.70(1) with critical temperature TC= 303.64(1) K for x = 0 while β= 0.389(1), γ= 1.334(1) and δ= 4.441(1) with TC= 330.84(1) K for x = 1. Further, the magnetization data in the vicinity of TC satisfies the magnetic scaling equations of state characteristic of a second-order phase transition. The magnetocaloric performance is reflected through maximum entropy change −ΔSmmax(T) ∼ 5.0(2.9) J kg−1 K−1; refrigerant capacity RC ∼ 505(302) J kg−1 and temperature-averaged entropy TEC(10 K) ∼ 4.92(2.28) J kg−1 K−1 at an applied field of 5 T for x = 0(1) ribbons, respectively. −ΔSmmax(T) embracing the critical region is found to be well-described by the critical exponents that are consistent with those determined by the modified Arrott plots and Kouvel–Fisher analyses. Renormalization group calculations further confirm that Mn5Ge3 and Mn4FeGe3 systems behave as 3D Ising and 3D Heisenberg ferromagnets in the critical region wherein short-range extended magnetic interactions decay as J(r) ≈ r−4.995 and r−4.895 with intermoment distance, respectively. Ferromagnetic resonance study reveals that with the introduction of Fe, the magnetocrystaline anisotropy (Ku∼1.4×106 erg/cm3) of Mn5Ge3 gets suppressed so much so that the system exhibits a crossover from 3D Ising to 3D Heisenberg universality class in the critical region.