Effect of Mn/Fe ratio on the Magnetic and Magnetocaloric Properties of Hexagonal Mn_2-<i>x</i>Fe_1+<i>x</i>Ge (0 ≤ <i>x</i> ≤ 1) Heusler Alloys

In this work, we synthesized bulk Mn_2-xFe_1+xGe (0 ≤ x ≤ 1) by arc melting and Mn₂FeGe melt-spun ribbons by rapid solidification using the melt-spinning technique and investigated their structural, magnetic, and magnetocaloric properties. Room temperature X-ray diffraction analyses show that Mn₂FeGe crystallizes into the hexagonal DO₁₉ crystal structure with a small trace of a secondary phase. Mn₂FeGe was found to be ferrimagnetic (FIM) with saturation magnetization (M_S) values of ~ 1.7 µ_B/f.u. at ground state which is consistent with the value 2.0 µ_B/f.u. predicted by the Slater-Pauling rule. Substitution of Fe for Mn in bulk Mn_2-xFe_1+xGe resulted in a change of the magnetic ground state from FIM to ferromagnetic (FM) with a maximum M_S value of 5.1 µ_B/f.u. for x = 1.0. A tunable Curie temperature (T_C) in a wide range of about 200 K, including the near room temperature ones, was found in Mn_2-xFe_1+xGe which may be important for practical applications. Maximum magnetic entropy changes of - 3.1 Jkg^-1K^-1 (at µ₀ΔH = 5 T) was found at room temperature with a refrigerant capacity of 325 Jkg^-1 for x = 0.4.