The impact of disorder on the 4O-martensite of Ni–Mn–Sn Heusler alloy

We have performed a quantum-mechanical study of thermodynamic, elastic, magnetic and structural properties of four different ferrimagnetic states in Ni1.9375Mn1.5625Sn0.5 martensite. They are modeled by the four-layer modulated 4O structures with Mn-excess atoms randomly distributed in Ni and Sn sublattices. The Mn atoms at the Ni sublattice turn out to be decisive for both thermodynamic and magnetic properties. A reversal of the orientation of their local magnetic moments has a huge impact on the properties of the whole system. The lowest-energy configuration exhibits anti-parallel local magnetic moments of these Mn atoms with respect to the orientation of the total magnetic moment. By testing both elastic properties and phonon modes we conclude that the lowest-energy state is mechanically stable. Vibrational properties of individual atoms are found to be very sensitive to the chemical disorder.