Magnet properties of Mn₇₀Ga₃₀ prepared by cold rolling and magnetic field annealing

The remanence and coercivity of arc melted Mn₇₀Ga₃₀ can be substantially improved by cold rolling. For best performance the rolled material should be annealed at T=730 K in the presence of a magnetic field of 1 T. The so-obtained magnet has a remanence of 0.239 T and a coercivity of 1.24 T at room temperature. The underlying reason for the high coercivity and remanence is the increase of the content of a metastable ferrimagnetic D0₂₂ phase at the expense of the normally stable anti-ferromagnetic D0₁₉. Magnetic field significantly increases the nucleation rate of the ferromagnetic D0₂₂ phase that leads to grain size refinement and as a consequence of improving remanence and coercive field. - Highlights: • Alternative synthesis method for D0₂₂ phase formation in Mn–Ga is developed. • Effect of cold rolling and annealing on magnetic properties of Mn₇₀Ga₃₀ is examined. • Small magnetic fields are sufficient to accelerate nucleation of the D0₂₂ phase