Magnetoelastic coupling and field-induced metamagnetism in the cubic Heusler alloy Mn_1.7Fe_1.3Si

We present a systematic study of the structural, magnetic, and transport properties of the cubic Heusler alloy Mn_1.7Fe_1.3Si. Room-temperature x-ray diffraction and temperature-dependent neutron powder diffraction confirm long-range cubic L2₁ordering, with no crystallographic phase transition down to 20 K. Magnetization measurements reveal a paramagnetic-ferromagnetic/ferrimagnetic transition atTC= 85 K, followed by a spin-reorientation transition between 65 K and 55 K. Neutron diffraction shows that long-range antiferromagnetic (AFM) order develops only below 55 K, stabilizing a canted AFM ground state. Anomalies in the temperature dependence of the unit-cell volume across magnetic transitions provide clear evidence of magnetoelastic coupling. Electrical resistivity measurements confirm metallic behaviour. At low temperatures, magnetization and magnetotransport data reveal a field-induced metamagnetic transition accompanied by irreversibility, metastability, and magnetic phase coexistence, leading to a low-field coexistence region in theH - Tphase diagram below 2.5 T. Notably, the metamagnetic transition is purely magnetic and occurs without any structural transformation. These results clarify the complex magnetic behaviour of Mn_1.7Fe_1.3Si and highlight the role of spin-lattice coupling in Mn-based Heusler alloys.