Tunneling Anisotropic Magnetoresistance in Multilayer-(Co/Pt)/AlOx/PtStructures

We report observations of tunneling anisotropic magnetoresitance (TAMR) in vertical tunnel devices with a ferromagnetic multilayer-($\mathrm{Co}/\mathrm{Pt}$) electrode and a nonmagnetic Pt counterelectrode separated by an ${\mathrm{AlO}}_x$ barrier. In stacks with the ferromagnetic electrode terminated by a Co film the TAMR magnitude saturates at 0.15% beyond which it shows only weak dependence on the magnetic field strength, bias voltage, and temperature. For ferromagnetic electrodes terminated by two monolayers of Pt we observe order(s) of magnitude enhancement of the TAMR and a strong dependence on field, temperature and bias. The discussion of experiments is based on relativistic ab initio calculations of magnetization orientation dependent densities of states of Co and $\mathrm{Co}/\mathrm{Pt}$ model systems.