High energy product of isotropic bulk Sm-Co/α-Fe(Co) nanocomposite magnet with multiple hard phases and nanoscale grains

Abstract

Nanocomposite magnets consisting of hard and soft magnetic phases have potential applications to be the next generation of permanent magnets with very high energy product and less expensive rare-earth elements. But it is still a big challenge to obtain bulk magnets with ideal microstructure and high performance. In this work, two - step warm processing at relative low temperatures had been adopted to obtain nearly theoretical density bulk nanocomposite magnets from amorphous/nanocrystalline powder precursors. Novel nanostructures consisting of multiple Sm-Co hard phases (SmCo5 as main phase, SmCo3, SmCo7, Sm2Co17 as minor phases) and 25 wt% α-Fe(Co) soft phase, nanoscale grain size below 20 nm for both the hard phase and soft phase, and the diffusion of Fe and Co compositions had been obtained in bulk isotropic magnets. Besides the ideal nanostructures, a high coercivity of 5.9 kOe, Mr/Ms value of 0.78 and a high square degree of demagnetization curve S = 0.47 were obtained. All of these factors together brought a new record-high energy product (BH)max of 23.6 MGOe. These results make an important step toward fabricating novel nanostructure with high performance.