Improving the energy product of hard magnetic materials

Abstract

A route toward enhancing the energy product $(\mathrm{BH}{)}_{\mathrm{max}}$ of permanent magnetic materials, at room temperature, based on ferromagnetic-(FM-) antiferromagnetic (AFM) exchange interactions has been developed. The exchange coupling, which is induced by ball milling hard magnetic ${\mathrm{SmCo}}_{5}$ with AFM NiO powders, results in an enhancement of coercivity ${H}_{C}$ and squareness ratio ${M}_{R}{/M}_{S}$ (remnant-saturation magnetizations), which depends on the FM:AFM ratio and the processing conditions. However, the presence of the AFM in the composite results also in a competing effect, i.e., reduction of the overall saturation magnetization, which decreases $(\mathrm{BH}{)}_{\mathrm{max}}.$ Nevertheless, it has been found that after an optimization of the FM:AFM ratio and the milling conditions it is possible to achieve an improvement of $(\mathrm{BH}{)}_{\mathrm{max}}.$