Understanding High Coercivity in ThMn12-Type Sm-Zr-Fe-Co-Ti Permanent Magnet Powders through Nanoscale Analysis

TL;DR

This study investigates how high-temperature processing enhances coercivity in ThMn12-type Sm-Zr-Fe-Co-Ti permanent magnet powders by reducing grain and twin boundaries, with nanoscale analysis revealing the underlying microstructural mechanisms.

Contribution

It provides new insights into the microstructural evolution during processing and its impact on coercivity in these advanced permanent magnets.

Findings

Coercivity increases from 0.45 T to 1.26 T with higher processing temperature.

High-temperature processing reduces grain and twin boundary densities.

Ostwald ripening explains boundary reduction and improved magnetic properties.

Abstract

ThMn12-type (Sm,Zr)1(Fe,Co,Ti)12 compounds show great potential for permanent magnets. Magnetically hard anisotropic powders prepared via reduction-diffusion exhibit a significant increase in coercivity from 0.45 T to 1.26 T as the processing temperature is raised from 990{\deg}C to 1220{\deg}C. Structural and microchemical analyses at high-resolution reveal that high-temperature processing annihilates grain boundaries (GBs) and reduces the density of twin boundaries (TBs), which are defects acting as weak links limiting the coercivity in the 1:12 system. Ostwald ripening is proposed as the mechanism behind the reduction of GB and TB densities at higher temperature, driven by the reduction in interfacial energy and enhancing atomic structural uniformity.