Two-dimensional zero thermal expansion in low-cost Mn_xFe_5−xSi₃ alloys via integrating crystallographic texture and magneto-volume effect

Zero thermal expansion (ZTE) alloys have unique aspects in the application of the engineering of precise dimensional control. However, the harsh conditions to realize ZTE, i.e., appropriate coupling among spin, lattice, and charge upon heating, have limited the ZTE alloys by very few numbers of species. In this work, we report a route to achieving two-dimensional (2D) ZTE behavior by regulating crystallographic texture and magneto-volume effects (MVEs) in volumetric positive thermal expansion alloys. This is illustrated in a series of Mn_xFe_5−xSi₃ compounds by those earth-abundant elements. As a result, a 2D ZTE performance with a coefficient of thermal expansion α_l = 0.45 × 10⁻⁷ K⁻¹ over a broad temperature window of 10–310 K was observed in MnFe₄Si₃. The experimental results by synchrotron X-ray diffraction, neutron diffraction, microscopy, and magnetization measurements reveal that such a ZTE behavior is strongly coupled with fiber crystallographic texture and magnetic moment at the crystallographic 6g site that dominates MVEs in the a-b plane. The competition between ferromagnetic Fe_4d-Fe_6g (J_FM) and antiferromagnetic Mn_4d-Mn_6g (J_AFM) interactions makes the Mn_1.5Fe_3.5Si₃ and Mn₂Fe₃Si₃ compounds show mixed magnetism and negative thermal expansion (NTE). The integral approach presented here can be used to extend the scope of ZTE/NTE species in other magnetic or ferroelectric materials.