Origins of the significant improvement in nanocrystalline Samarium-Cobalt's magnetic properties when doping with Niobium

Highlights: • The coercivity of SmCo₇ ribbon is greatly enhanced by Nb-doping. • Nb resides at the 2e sites and thus stabilizes the SmCo₇ structure and enhances K₁. • Nb-doping refines the microstructure of SmCo₇ ribbon. • Enhanced coercivity results from increased K₁ and refined microstructure. • This work provides useful information to predict magnetic properties of materials. - Abstract: SmCo₇-based compounds are prototypical rare-earth based hard magnetic materials that are the backbone of numerous devices and applications. We have found that by doping the SmCo₇ phase with Niobium (e.g. SmCo_6.7Nb_0.3), the enhanced coercivity being measured. Using a combination of microstructural and compositional characterization techniques with ab initio calculations, we find that the Nb-doping stabilizes the nanocrystalline nature of the material by residing at the 2e site of the SmCo₇ structure, decreases the average grain size, and substantially increases the magnetocrystalline anisotropy constant (K) (e.g. from 1.25 × 10⁷ erg/cm³ for SmCo₇ to 1.40 × 10⁷ erg/cm³ for SmCo_6.7Nb_0.3). A significant enhancement in coercivity with Nb doping is attributed to the increased K and the reduced grain size