Tunable thermal expansion via the magnetic phase competition in kagome magnets

Negative thermal expansion materials can solve the challenge of mismatched coefficients of thermal expansion of components in precision instruments, thereby improving the thermal shock resistance of devices. The adjustment of negative thermal expansion performance can improve the universality of its application. In this work, tunable thermal expansion has been achieved in Hf1−xTaxFe2 kagome magnets via magnetic phase competition. The transition from ferromagnetism to antiferromagnetism results in a sharp volume shrinkage of Hf0.83Ta0.17Fe2 within a narrow temperature range of 190–230 K, which limits its practical application. As the Ta content decreases, the ferromagnetic ground state becomes more robust and eventually suppresses the antiferromagnetism completely, achieving a negative thermal expansion in Hf0.88Ta0.12Fe2 caused by the ferromagnetic to paramagnetic transition over a wide temperature region and containing room temperature (αV = −37.63 × 10−6 K−1, 250–350 K). This work realizes the regulation of negative thermal expansion through magnetic phase competition, which provides guidance for the regulation of thermal expansion of magnetic materials in the future.