Magnetic properties of embedded ferromagnetic contacts to silicon for spin injection

We investigate the magnetic properties of arrays of sputter-deposited, Co70Fe30/Ni80Fe20 and Co40Fe40B20 contacts to silicon, embedded into 42 nm thick SiO2 dielectric. The contacts have rectangular shapes with blunt edges, sub-micrometre width and different aspect ratios. They are deposited either directly on silicon, forming Schottky junctions or on top of an MgO tunnel barriers with varying thickness. The MgO and CoFeB electrode are amorphous while the CoFe/NiFe bilayer is polycrystalline. The magnetization switching characteristics are studied by means of the magneto-optical Kerr effect and magnetic force microscopy. The switching field and its distribution within the array are found to depend on the thickness of the MgO and the ferromagnet (FM). Switching is mostly determined by the contact's width by means of end domains formed at the blunt edges. An influence of the length for wider contacts is also demonstrated. Despite a small angle magnetization misalignment along the contact, the remanence is high in all cases. The switching characteristics are shown to deteriorate after high temperature annealing, especially for the amorphous CoFeB FM due to the onset of crystallization.