Magnetic BiMn-α phase synthesis prediction: First-principles calculation, thermodynamic modeling and nonequilibrium chemical partitioning

•First-principles calculations with Hubbard U correction and SQSs were employed.•Gibbs free energy function of individual phases was evaluated.•The magnetic field-T−x(Mn) dependent phase selections were predicted.•Single- or multiple-phase microstructure can be controlled by chemical partitioning.•The magnetic properties can be tailored by controlling the microstructures.