The effect of substrate bias on the properties of NiO/NiFe and NiO/CoFe exchange biased spin-valve sensors

The effect of substrate bias applied during the deposition of NiO on the properties of unshielded NiO/Ni₈₁Fe₁₉ and NiO/Co₈₇Fe₁₃ biased spin-valve sensors was investigated. The addition of substrate bias of -40 V increased the blocking temperature T_b from 100-190°C for NiO/NiFe biased spin valves, and from 70-190°C for NiO/CoFe biased spin valves. The thermal stability upon anneal increased with substrate bias from 150-200°C for NiO/NiFe biased spin-valve sensors, and from 200-280°C for NiO/CoFe biased spin-valve sensors. At an operating temperature of 80°C, sensor magnetoresistance decreases 15% from its room temperature value for NiO/CoFe sensors where NiO was deposited under -40 V bias. At this temperature, the sensor transfer curves are well linearized and Barkhausen noise free. NiO films prepared with varying substrate bias were examined by atomic force microscopy (AFM) and X-ray diffraction. Substrate bias decreases surface morphology and grain size of NiO, which probably contributes to the observed improvement of blocking temperature