Neutron diffraction and symmetry analysis of the martensitic transformation in Co-doped Ni2MnGa

WOS: 000519988900002 Martensitic transformations are strain driven displacive transitions governing the mechanical and physical properties in intermetallic materials. This is the case in Ni2MnGa, where the martensite transition is at the heart of the striking magnetic shape memory and magnetocaloric properties. Interestingly, the martensitic transformation is preceded by a premartensite phase, and the role of this precursor and its influence on the martensitic transition and properties is still a matter of debate. In this work we report on the influence of Co doping (Ni50-xCoxMn25Ga25 with x = 3 and 5) on the martensitic transformation path in stoichiometric Ni2MnGa by neutron diffraction. The use of the superspace formalism to describe the crystal structure of the modulated martensitic phases, joined with a group theoretical analysis, allows unfolding the different distortions featuring the structural transitions. Finally, a general Landau thermodynamic potential of the martensitic transformation, based on the symmetry analysis, is outlined. The combined use of phenomenological and crystallographic studies highlights the close relationship between the lattice distortions at the core of the Ni2MnGa physical properties and, more in general, on the properties of the martensitic transformations in the Ni-Mn based Heusler systems. Departments of Excellence' program of the Italian Ministry for Education, University and Research (MIUR, 2018-2022) The authors acknowledge the Science and Technology Facilities Council for providing neutron beamtime on the WISH beamline. F.O. acknowledges Dr. Giovanni Romanelli for useful discussion. This work has benefited from the COMPHUB Initiative, funded by the `Departments of Excellence' program of the Italian Ministry for Education, University and Research (MIUR, 2018-2022).