Zero Thermal Expansion via the Unconventional Sublattice‐Magnetovolume Effect in Rare‐Earth Ferrimagnets

Abstract Zero thermal expansion (ZTE) alloys are critically needed in sophisticated modern industries, including telescope manufacturing, satellite technology, and semiconductor production, owing to their exceptional dimensional stability. In this study, high‐performance ZTE with a negligible coefficient of thermal expansion α v = 2.7 ppm K −1 over a broad temperature range of 10–220 K is discovered in ErCo 2.8 Fe 0.2 magnet. Owing to an unconventional sublattice‐magnetovolume effect in the Er atoms, the negative thermal expansion in Fe‐substituted ErCo 3− x Fe x magnets can be easily tuned to high‐performance ZTE. Moreover, the direct visualization of the magnetic transition in the predominant magnetization from the Er to the Co/Fe sublattices, as observed by the Lorentz transmission electron microscopy, further elucidates the manipulation mechanism behind the high‐performance ZTE. This study reports a convenient and effective strategy to optimize the thermal expansion characteristics of Er‐Co‐Fe magnets, which can guide future research that broadens the application scope of magnetic materials by leveraging the significant correlation between the magnetic properties and crystal structure of such systems.