High Magnetic Field Annealing of Mn-Ga Intermetallic Alloys

Mn-Ga alloys have shown promising hard magnetic properties, even though these alloys contain no rare-earth metals. However, much work is needed before Mn-Ga alloys become viable permanent magnets for applications. One of the challenges is to enhance the remanence. One technique to improve this property is applying a magnetic field during the heat treatment process. Magnetic annealing can promote phase transformation of the phases with high magnetic moment. This results in an increased remanence. Bulk samples of Mn-Ga alloys were made by mechanically alloying in order to create a nanostructured composite, followed by heat treatments in the presence of a 31 T magnetic field. The heat treatment temperatures were kept low in order to keep the refined microstructure. All the alloys exhibit hard magnetic properties at room temperature with large coercivity. This work reports findings of magnetic field annealed Mn-Ga bulk that exhibit high coercivities up to 19.4 kOe and increased remanence of 50% over the binary system, achieving values up to 6.9 emu/g. This is the highest coercivity reported in bulk Mn-Ga samples.