Anisotropy of spin polarization and spin accumulation in Si/Al2O3/ferromagnet tunnel devices

The contribution of the spin accumulation to tunneling anisotropy in Si/Al2O3/ferromagnet devices was investigated. Rotation of the magnetization of the ferromagnet from in-plane to perpendicular to the tunnel interface reveals a tunneling anisotropy that depends on the type of the ferromagnet (Fe or Ni) and on the doping of the Si (n or p type). Analysis shows that different contributions to the anisotropy coexist. Besides the regular tunneling anisotropic magnetoresistance, we identify a contribution due to anisotropy of the tunnel spin polarization of the oxide/ferromagnet interface. This causes the spin accumulation to be anisotropic, i.e., dependent on the absolute orientation of the magnetization of the ferromagnet.