Correlating Magnetic Damping and Microstructure in "Half Metal" Thin Films

Highly spin-polarised materials show great promise in applied spintronics as spin-filters and spin transfer torque magnetic random-access memory devices for data storage. However, controllable magnetisation switching requires materials with a low Gilbert damping parameter and stable magnetic properties at room temperature. Two highly spin-polarised magnetic materials with critical temperatures well above room temperature are characterised using a series of structural and magnetic analysis techniques. Correlation between the magnetic damping and microstructure is observed in both Fe3O4 and Co2FeAl0.5Si0.5 samples and both are seen to improve structurally and show more favourable damping parameters with annealing.
Annealing Fe3O4 in CO/CO2 is shown to reduce the antiphase boundary density and decrease the two-magnon scattering-like extrinsic damping effects. The quality of the sample structure and the stoichiometry is also seen to improve considerably after the annealing although the defects are not completely eliminated. An anomalous peak in the damping of the annealed film is observed at 10GHz
Co2FeAl0.5Si0.5 grown on germanium and silicon substrates is seen to also improve with thermal annealing. The Gilbert damping is seen to be lower in the as-grown scheme using the silicon substrate but greater reduction of damping post-annealing is seen on germanium. In both cases the B2 order is observed in the Co2FeAl0.5Si0.5 thin films, and intermixing between the sample and substrate observed above 500oC is sufficient to disrupt the crystal structure and introduce significant extrinsic damping effects which increase the total damping. This prevents the Co2FeAl0.5Si0.5 from reaching the more desirable L21 structure.