Structural and magnetic properties of Fe11Mn2Ga3: an off-stoichiometric Heusler alloy

This work investigates the structural and magnetic properties of the off-stoichiometric Heusler alloy Fe₁₁Mn₂Ga₃. X-ray diffraction confirms a face-centered cubic L2₁ structure with significant chemical disorder. Magnetic characterization reveals a complex phase diagram with two distinct transitions: a Curie temperature at T m2 =309 K and a magnetic reorientation at T m1 =167 K, below which antiferromagnetic interactions dominate, evidenced by a reentrant decrease in magnetization. This behavior yields a bifunctional magnetocaloric response, with a direct effect near T m1 and an inverse effect near T m2 . Mössbauer spectroscopy confirms a ferrimagnetic state at room temperature and provides microscopic evidence for the development of non-collinear magnetism at low temperatures. The novelty of these results lies in the consequences of the strong Fe-rich off-stoichiometry, which stabilizes chemical disorder and shifts the balance beteween competing ferromagnetic and antiferromagnetic interactions to unusually high temperatures. The results demonstrate that strategic off-stoichiometry is a powerful tool for stabilizing disordered states and engineering novel magnetic functionality in Heusler alloys.