Effect of high pressure torsion on magnetic properties and corrosion resistance of MnBi/NdFeB composite magnets

Abstract

The MnBi/NdFeB composite magnets have been fabricated by high pressure torsion (HPT). The effects of NdFeB content, torsional pressure and torsional degree on the microstructures, magnetic properties, and corrosion resistance of the MnBi/NdFeB composite magnets are systematically investigated. The results show that the remanent magnetization (Mr) of MnBi/NdFeB composite magnets increases with the Nd2Fe14B content. A peak value of the maximum energy product ((BH)max) = 5.61 MGOe is obtained while the Nd2Fe14B content is 75 wt%. Addition of MnBi increases the coercivity temperature coefficient and the density of MnBi/NdFeB composite magnets. The MnBi/NdFeB composite magnets prepared by HPT show perpendicular anisotropy, which can be explained by the (0kl) texture in the perpendicular direction observed by TEM. With the increase of degree of HPT, the intrinsic coercivity (Hcj) difference between perpendicular direction and parallel direction is more obvious, the (0kl) texture is enhanced by the degree of HPT. The first-order reversal curve (FORC) demonstrates that MnBi/NdFeB composite magnets exhibits weaker exchange coupling compared with pure MnBi magnet. Besides, a remarkably improvement in electrochemical stability for the MnBi/NdFeB composite magnet is achieved with the MnBi added.