Transforming Thermal Expansion from Positive to Negative: The Case of Cubic Magnetic Compounds of (Zr,Nb)Fe₂

Negative thermal expansion (NTE) is an intriguing property for not only fundamental studies but also technological applications. However, few NTE materials are available compared with the huge amount of positive thermal expansion materials. The discovery of new NTE materials remains challenging. Here we report a chemical modification strategy to transform thermal expansion from positive to negative in cubic magnetic compounds of (Zr,Nb)Fe₂ by tuning the magnetic exchange interaction. Furthermore, an isotropic zero thermal expansion can be established in Zr_0.8Nb_0.2Fe₂ (α_l = 1.4 × 10^-6 K^-1, 3-470 K) over a broad temperature range that is even wider than that of the prototype Invar alloy of Fe_0.64Ni_0.36. The NTE of (Zr,Nb)Fe₂ is originated from the weakened magnetic exchange interaction and the increased d electrons of Fe by the Nb chemical substitution, so that the magnetovolume effect overwhelms the contribution of anharmonic lattice vibration.