Magneto-electric Tuning of Pinning-Type Permanent Magnets through Atomic-Scale Engineering of Grain Boundaries

TL;DR

This study demonstrates that hydrogen-induced modifications at grain boundaries can reversibly enhance coercivity in Sm2Co17-based magnets, revealing a new pathway for optimizing permanent magnets through atomic-scale engineering.

Contribution

It introduces a magneto-electric approach to reversibly tune coercivity by hydrogen charging at grain boundaries, highlighting the critical role of grain boundary engineering in permanent magnets.

Findings

Hydrogen segregation at grain boundaries significantly increases coercivity.

Reversible coercivity tuning of ~1.3 T achieved with ~1 V voltage.

Grain boundary modifications dominate magnetization reversal behavior.

Abstract

Pinning-type magnets maintaining high coercivity, i.e. the ability to sustain magnetization, at high temperature are at the core of thriving clean-energy technologies. Among these, Sm2Co17-based magnets are excellent candidates owing to their high-temperature stability. However, despite decades of efforts to optimize the intragranular microstructure, the coercivity currently only reaches 20~30% of the theoretical limits. Here, the roles of the grain-interior nanostructure and the grain boundaries in controlling coercivity are disentangled by an emerging magneto-electric approach. Through hydrogen charging/discharging by applying voltages of only ~ 1 V, the coercivity is reversibly tuned by an unprecedented value of ~ 1.3 T. In situ magneto-structural measurements and atomic-scale tracking of hydrogen atoms reveal that the segregation of hydrogen atoms at the grain boundaries, rather than the change of the crystal structure, dominates the reversible and substantial change of coercivity. Hydrogen lowers the local magnetocrystalline anisotropy and facilitates the magnetization reversal starting from the grain boundaries. Our study reveals the previously neglected critical role of grain boundaries in the conventional magnetisation-switching paradigm, suggesting a critical reconsideration of strategies to overcome the coercivity limits in permanent magnets, via for instance atomic-scale grain boundary engineering.