Thermal stability of NiMn spin valve heads

The thermal stability of NiMn-based spin valves was studied both at the coupon level and in full read/write heads. In the coupons, the blocking temperature distribution showed no component below 150°C. As a result, the exchange field at elevated temperature was found to increase with time (because of improved chemical ordering of the NiMn layer), and irreversible losses in the ΔR/R response were observed only above 250°C (because of layer interdiffusion). If a 10% drop in ΔR/R amplitude is used as a criterion to calculate time to failure, the NiMn heads should have several hundred years of lifetime at 150°C operating temperature. Full read/write heads showed linear response with read-back amplitudes above 2 mV/μm at 6-mA operating current. In contrast to most other giant magnetoresistance heads, the output of the head remains the same after heating with a high bias current and degrades only with the shorting of the stripe. All these properties make NiMn superior to other antiferromagnets for spin valve head applications