Tuning magnetic and electronic properties by Mn excess and deficiency in Ni2Mn1+xSn1-x Heusler alloys

This work presents a first-principles investigation into the effects of Mn excess and deficiency on the structural, electronic, and magnetic properties of Ni 2 Mn 1+x Sn 1-x full-Heusler alloys, focusing on off-stoichiometric compositions with x ranging from −0.2 to 0.2. The calculations are performed within the spin-polarized relativistic Korringa-Kohn-Rostoker method combined with the coherent potential approximation (CPA), enabling a consistent treatment of substitutional disorder. We analyze the stability of L2 1 structures (including composition-induced antisite disorder for off-stoichiometric compositions) as well as the partially disordered B2 and fully disordered A2 phases. Magnetic properties are evaluated in terms of local moments, Heisenberg exchange interactions, and Curie temperatures. Particular attention is devoted to the calculation of the spin-wave stiffness using a real-space formalism within CPA, including a controlled treatment of long-range exchange interactions via damping and extrapolation. The results provide a comprehensive description of how compositional deviations and atomic disorder affect magnetic exchange and spin dynamics in Ni-Mn-Sn alloys, offering insight into the mechanisms governing their magnetic stability and the interplay between chemical disorder and magnetic properties in Heusler alloys.