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

• 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.

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. SmCo6.7Nb0.3), 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 SmCo6.7Nb0.3). A significant enhancement in coercivity with Nb doping is attributed to the increased K and the reduced grain size.