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

• 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.

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.