Thermal sprayed thick-film anisotropic magnetoresistive sensors

Ni₈₀Fe₂₀ and Ni₈₀Co₂₀ alloys anisotropic magneto-resistive sensor films were deposited by plasma spray. The resistivity (ρ) of the films is determined to be 40-70 μΩ·cm in the as-sprayed state. The oxygen impurity dissolved in the metal acts as a strong scattering center and results in higher resistivity. The ρ of sensor film improves significantly with thermal annealing up to 500°C and it remains constant for further increase in temperature. The dissolved oxygen precipitates out as oxide phase during heat treatment and that reduces the scattering. The ρ values are 19 and 22 μΩ·cm for permalloy and NiCo alloy films, respectively, which are close to bulk values. The anisotropic magnetoresistance (AMR) effect is found to be increased by a factor of 2 in both the permalloy and the NiCo sensors. The ΔR/R values are increased from 2.0% to 4.0% and 2.6% to 5.8%, respectively, for permalloy and NiCo sensors.