Enhanced saturation magnetization in perpendicular L1–MnAl films upon low substitution of Mn by 3d transition metals

Abstract

In order to enhance the saturation magnetization (Ms) of a L10−MnAl alloy, which is a promising candidate for use in rare-earth free permanent magnets, this work assesses perpendicular L10−MnAl films in which Mn is substituted by the 3d transition metals (TMs) Fe, Co, Ni, or Cu. In the films for which the TM is Fe or Ni, the lattice constant, a, of the L10−(Mn, TM)Al phase increases from 0.390 to 0.397 nm with a substitution amount, x, of 5 at. %. Simultaneously, the lattice constant, c, decreases from 0.355 to 0.350 nm, such that the lattice ratio, c/a, changes from 0.91 to 0.88. Upon increasing x to more than 5 at. %, an unknown phase (either Mn or another Mn−Al phase) forms together with the L10−(Mn, TM)Al phase. The Ms of the MnAl film increases from 360 to more than 400 emu/cm3 with an increasing x when substituting Fe or Ni for Mn. In addition, although a MnAl film without substitution shows a Ms of 360 emu/cm3 and a Hc of 4.1 kOe, a MnAl film substituted with Fe at x = 2.5 at. % exhibits a Ms of 400 emu/cm3 and a Hc of 3.8 kOe. These results suggest that the lattice changes induced in the L10−MnAl alloy upon substituting Fe or Ni for Mn, corresponding to an expansion of the interatomic distance between (Mn, TM) atoms, are an effective means of enhancing the Ms value of the alloy.