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 degrees C for NiO/NiFe biased spin valves, and from 70-190 degrees C for NiO/CoFe biased spin valves, The thermal stability upon anneal increased with substrate bias from 150-200 degrees C for NiO/NiFe biased spin-valve sensors, and from 200-280 degrees C for NiO/CoFe biased spin-valve sensors, At an operating temperature of 80 degrees 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.