Interplanar Magnetic Orders and Symmetry-Tuned Zero Thermal Expansion in Kagomé Metal (Zr,Ta)Fe₂

Abstract

An alternative strategy was proposed for a family of kagomé metals (Zr,Ta)Fe2 to tailor thermal expansion by utilizing thermodynamic phase stability rather than by conventionally altering chemical composition. An isotropic zero thermal expansion (ZTE, αl ∼ + 0.9 × 10-6 K-1, 10-430 K) is demonstrated in high-quality cubic ingots over a superior magnetic ordering temperature window up to 430 K. A combined neutron diffraction, Mössbauer spectrum, and theoretical calculations analysis fundamentally uncover that the magnetic ordering of adjacent kagomé Fe-layers intimately changes from antiferromagnetic to ferromagnetic on transforming from hexagonal to cubic symmetry. Due to lifting of the interplanar magnetic frustration, magnetic ordering is enhanced and enables a strong temperature-induced longitudinal spin fluctuations, thus leading to large magnetic compensation for lattice thermal expansion.