Investigation of local surrounding of Mn atoms in Ni-Mn-Ga Heusler alloy using nuclear magnetic resonance

The local environment of Mn atoms in stoichiometric and off-stoichiometric (with Mn excess) Ni-Mn-Ga Heusler alloys was investigated using Nuclear Magnetic Resonance (NMR) and interpreted with the help of Density Functional Theory (DFT) methods. In cubic austenite, the significant amount of structural defects was observed in ⁵⁵Mn NMR experiments and interpreted using DFT calculations as individual antisite defects or defects accompanying anti-phase boundaries. The spectrum of non-modulated martensite was similar to that of austenite, albeit with increasing disorder due to excess Mn. In 10M modulated martensite, the main lines were split. The splitting is ascribed to structural modulation and quantitative analysis shows that the amplitude of modulation evolves with temperature and its magnitude is in agreement with diffraction data.