Enhancing coercivity through grain boundary phase modification in SmxFe10V2

Abstract

ThMn12-type Sm(FeV)12 magnets with high coercivity (Hc) demonstrate promising potential as alternative rare-earth-lean permanent magnets. This study delves into the microstructure and magnetic properties influenced by the Sm content in the SmxFe10V2 (x = 1.4–1.9) alloy. High-density SmFe10V2 bulks were prepared through a jet-milling process, followed by high-pressure pressing and heat treatment. Upon increasing the Sm content beyond 1.6, the heat-treated bulks exhibited a predominant ThMn12 phase, accompanied by a secondary phase – Sm oxides. Additionally, Sm played a pivotal role in influencing the ThMn12 crystal structure, with the c/a value reaching the smallest in the Sm1.7Fe10V2 bulk. This change contributed to heightened anisotropy constants and Tc values. The introduction of an amorphous Sm-rich grain boundary phase, with the thickness of 1.2 nm, was observed in bulks within a specific Sm content range, influenced by the heat-treatment time. Notably, this phase was absent in bulks with insufficient or excessive Sm. The grain boundary phase had a substantial impact on improving Hc, reaching 10.6 kOe in the Sm1.7Fe10V2 bulk heat-treated for 25 min. However, Hc exhibited a gradual decrease with prolonged heat treatment, attributed to the evaporation of Sm leading to the disappearance of the grain boundary phase. This nuanced relationship underscores the importance of optimizing heat treatment conditions to harness the full potential of ThMn12-type Sm(FeV)12 magnets for enhanced Hc.