Probing Collinear and Non-Collinear Magnetic Configurations of 3d Transition Metal Adlayers Supported on Mn-Ga Terminated Ni₂MnGa (001) Surface

The study of magnetic adlayers supported on magnetic and nonmagnetic elemental surfaces has attracted lot of attention for their interesting and sometimes complex magnetic properties. Here, we have carried out electronic structure calculations to study and analyze the collinear and non-collinear magnetic ordering of a monolayer of transition metal (TM) atoms (Cr, Mn,Fe, Co,Ni), on the Mn-Ga terminated surface of ferromagnetic Heusler alloy Ni₂MnGa. We find that all of these adatoms on the surface tend to have collinear configurations . However, only for the Cr adatoms we find a local minimum of energy for the non-collinear magnetic ordering, where the two Cr adatoms are AFM coupled to each other and their magnetization axes are rotated with a rotation angle 72^° and 79^° with respect to the Z axis. Further, we observe that there are two sets of collinear configurations (1) the Cr and Mn atoms which are anti-ferromagnetically (AFM) coupled, whereas (2) the Fe , Co and Ni adatoms which are ferromagetically (FM) coupled to the substrate. This behavior can be understood, from the Alexander-Anderson model. We further probe the dependence of two parameters, namely, surface termination and thickness of the adlayers, on the collinear magnetic properties for two adatoms, Cr and Fe.