On the remarkable coercivity in MnBi by microstructural engineering

MnBi materials with different microstructures were prepared by severe plastic deformation using different processing conditions. The coercivity can be controlled by tuning the grain size, defect density, and the phase distribution of the MnBi in the remaining matrix. A maximum room-temperature coercivity of 1.8 T was achieved. The essential reason for the high coercivity is the size of the MnBi grains magnetically isolated by the matrix. Coercivity decreases as grain size and phase amount increase. Coercivity further declines by annealing despite similar grain size, indicating a declining influence of domain wall pinning and a coercivity mechanism influenced by the microstructure.