High-Temperature Itinerant Ferromagnetism in a $$\sigma $$-Phase High-Entropy Alloy (FeCr)$$_{0.67}$$(MnNiV)$$_{0.33}$$

Abstract A $$\\sigma $$ σ -phase high-entropy alloy with nominal composition (FeCr) $$_{0.67}$$ 0.67 (MnNiV) $$_{0.33}$$ 0.33 has been synthesized and investigated using structural, magnetic, thermodynamic, and local spectroscopic techniques. Room-temperature X-ray diffraction confirms the stabilization of the $$\\sigma $$ σ -phase lattice, characterized by five crystallographically inequivalent atomic sites randomly occupied by multiple transition metal elements. DC magnetization measurements reveal the onset of ferromagnetic order at $$T_{\\text{C}} = 322(2)$$ T C = 322 ( 2 ) K, exceeding Curie temperatures reported so far for $$\\sigma $$ σ -phase alloys. Despite the high ordering temperature, the magnetic response is dominated by a small spontaneous moment, pronounced field dependence, and lack of saturation in high magnetic fields, indicating a magnetically itinerant ground state. Specific heat data show a broad magnetic contribution near $$T_{\\text{C}}$$ T C together with a low-temperature excess term, pointing to strong spin fluctuations and slow magnetic dynamics. $$^{57}$$ 57 Fe Mössbauer spectroscopy does not reveal well-resolved magnetic splitting, indicating that the local magnetic polarization at Fe sites remains weak even within the magnetically ordered state. Taken together, these results establish the coexistence of long-range magnetic order and strong itinerancy in a chemically complex $$\\sigma $$ σ -phase alloy, highlighting high-entropy design as an effective route for realizing high-temperature itinerant ferromagnetism in chemically disordered and structurally complex crystal structures.