Flexible Spin Orientation Optimized Lower‐Density Zero Thermal Expansion in the Sc‐Based Kagome Magnets

A variety of lightweight, high-precision engineering approaches are urgently required to decrease the density of metallic components exhibiting zero thermal expansion (ZTE). Scandium, the lightest rare-earth element, plays a unique role in the emergent quantum orders of Kagome metals. Here, we report the controlled design of interplanar magnetic order and thermal expansion in a family of Kagome (Sc,Ti)Fe₂ compounds. Optimizing the Sc-Ti-Fe ternary composition enables ZTE behavior up to room temperature (α_l = +0.18 × 10^-6 K^-1, 112-300 K) in Sc_0.4Ti_0.6Fe_2.4, together with a relatively low density of 6.56 g/cm³, which is much smaller than that of the documented ZTE alloys. Scanning transmission electron microscopy, Mössbauer spectroscopy, neutron powder diffraction, and theoretical calculations reveal that the extra positive magnetic exchange interactions of antisite Fe stabilize strong in-plane ferromagnetic order and suppresses spin reorientation from in-plane to out-of-plane upon heating. Local magnetic moments of Fe(2a) and Fe(6h) sites decrease successively over a wider temperature range, thus yielding such ZTE performance. The nearly isotropic ZTE of the ingot indicates its practical potential for advanced functional applications.