LAUSR

Zero‐thermal‐expansion (ZTE) alloys, as dimensionally stable materials, are urgently required in many fields, particularly in highly advanced modern industries. In this study, high‐performance ZTE with a negligible coefficient of thermal expansion av as small as 2.4 ppm K−1 in a broad temperature range of 85–245 K is discovered in Hf0.85Ta0.15Fe2C0.01 magnet. It is demonstrated that the addition of trace interstitial atom C into Ta‐substituted Hf0.85Ta0.15Fe2 exhibits significant capability to tune the normal positive thermal expansion into high‐performance ZTE via enhanced magnetoelastic coupling in stabilized ferromagnetic structure. Moreover, direct observation of the magnetic transition between ferromagnetic and triangular antiferromagnetic states via Lorentz transmission electron microscopy, along with corresponding theoretical calculations, further uncovers the manipulation mechanism of ZTE and negative thermal expansion. A convenient and effective method to optimize thermal expansion and achieve ZTE with interstitial C addition may result in broadened applications based on the strong correlation between the magnetic properties and crystal structure.