Effects of deposition temperature on magnetoresistance anisotropy of Ni-Co alloys

The magnetoresistance anisotropy of E-beam evaporated thin film samples of two Ni-Co alloys (50Ni- 50Co and 69Ni-31Co weight percentage) was studied as a function of substrate deposition temperature from 40°C to more than 200°C. The values of the magnetoresistance anisotropy are approximately 20% below bulk values at 40°C but increase monotonically to the accepted bulk values at 160°C. Subsequent vacuum annealing of the 40°C samples increased the magnetoresistance anisotropy nearly to bulk values. The thermal activation energy for changes in the magnetoresistance anisotropy (Δρ) and resistivity (ρ) was determined to be 1.40 ± 0.1 eV at 50Ni-50Co and 1.25 ± 0.1 eV at 69Ni-31Co. since the mechanism for changes of resistivity with annealing are well understood in terms of the crystallite size, the fact that the activation energies are the same for Δρ and ρ suggests a common mechanism, which further implies that an interaction of longer range than the spin-orbit interaction is at least partially responsible for the anisotropic magnetoresistance.