Thin film epitaxial [111] Co _50 Pt _50 : structure, magnetisation, and spin polarisation

Ferromagnetic films with perpendicular magnetic anisotropy are of interest in spintronics and superconducting spintronics. Perpendicular magnetic anisotropy can be achieved in thin ferromagnetic multilayer structures, when the anisotropy is driven by carefully engineered interfaces. Devices with multiple interfaces are disadvantageous for our application in superconducting spintronics, where the current perpendicular to plane is affected by the interfaces. Robust intrinsic PMA can be achieved in certain Co _x Pt _100-x alloys and compounds at any thickness, without increasing the number of interfaces. Here, we grow equiatomic Co _50 Pt _50 and report a comprehensive study on the structural, magnetic, and spin-polarisation properties in the L1_1 and L1_0 ordered compounds. Primarily, interest in Co _50 Pt _50 has been in the L1_0 crystal structure, where layers of Pt and Co are stacked alternately in the [100] direction. There has been less work on L1_1 crystal structure, where the stacking is in the [111] direction. For the latter L1_1 crystal structure, we find magnetic anisotropy perpendicular to the film plane. For the former L1_0 crystal structure, the magnetic anisotropy is perpendicular to the [100] plane, which is neither in-plane or out-of-plane in our samples. We obtain a value for the ballistic spin polarisation of the L1_1 and L1_0 Co _50 Pt _50 to be 47± 3% .