Realizing high-energy-product SmCo/α-Fe(Co) nanocomposite magnets with high soft phase fraction by component regulation

Forming nanocomposite magnetic materials composed of hard and soft phases is a promising way to enhance the energy product, which have great applications in energy conversion devices and clean energy generators, etc. Especially, SmCo-based nanocomposite magnets are attractive for their exceptionally high Curie temperature and high temperature applications. However, its microstructure control with a high soft phase fraction is of great challenge. Here, we report a strategy to fabricate SmCo/α-Fe(Co) nanocomposite bulk magnets with a soft phase content of over 30 wt%. The resultant (SmCo₇ + SmCo₃)/α-Fe(Co) nanostructure exhibits high soft phase content (31 wt%), small grain size (∼9 nm), and strong texture of the two hard phases (SmCo₇: I₍₀₀₂₎/I₍₁₁₁₎ = 0.96, SmCo₃: I₍₀₀₁₂₎/I₍₁₁₆₎ = 0.77). The good microstructure results in a large coercivity (H_ci = 4.2 kOe) and a high remanence ratio (M_r/M_s = 0.93), achieving an impressive energy product of 28.3 MGOe. This value is 51% larger than that of the SmCo₇/α-Fe(Co) nanocomposite magnets (18.7 MGOe) and 66% higher than that of the highest reported value (17 MGOe) of the SmCo₃/Fe(Co) nanocomposite magnets. The purposeful introduction of Fe, Cu, and Zr elements in the SmCo hard magnetic phase precursor allows the Fe and Co atoms to diffuse from the hard phase to the soft phase, thus obtaining a high soft phase fraction. These results represent an important step to novel SmCo nanocomposite magnets with excellent performance.