Fine tuning of the magnetic properties in Mn3-x Co x Ga Heusler films near the critical regime

Highlights: • Critical regime during the transition from hard ferrimagnetic tetragonal to soft ferrimagnetic cubic in Co-substituted Mn3Ga. • Dramatic reduction of the coercive field on remaining perpendicular magnetic anisotropy in the critical regime. • Compensation point near this critical regime due to a large reduction of the Co moments when substituted in Mn₃Ga. -- Abstract: Tunability of structural and magnetic properties of Mn_3-xCo_xGa films is presented by Co substitution, where critical behavior emerges 0.37 ≤ x ≤ 0.56 exhibiting a transition from tetragonal hard ferrimagnetic with perpendicular magnetic anisotropy (PMA) to a cubic soft ferrimagnetic phase with in-plane magnetic anisotropy (IMA). In the critical regime, coexisting state of tetragonal and cubic phases possesses significantly low coercive field (H_C = 1.9 kOe) with relatively low saturation magnetization (M_S = 100~150 emu/cc) while maintaining the PMA. From first-principles calculations, moments of two Mn sites do not change upon Co substitution. However, moments of substituted Co almost vanish in tetragonal while giving around 1 μ_B in cubic phase, which agrees with overall M_S behaviors of the experimental results. These findings not only uncover the hidden magnetic state in Mn_3-xCo_xGa by altering the parallel and antiparallel coupling between Mn and Co, but also provide an additional degree of freedom for spintronic applications using Mn-based Heusler compounds.