Improvement of thermal stability and magnetoresistance recovery of Tb25Co75 biased spin-valve heads

The thermal stability of TbCo exchange biased spin valve sensors has been extended to 230 °C, by using a Co pinned layer rather than NiFe. Magnetoresistance (MR) remains essentially stable up to annealing temperatures TA of 230 °C and degrades to 1% at TA=240 °C. Providing TA does not exceed 230 °C, any loss in the MR signal can be fully recovered by applying a field perpendicular to the film plane. This improved thermal stability allows processing at higher temperatures. The unidirectional exchange in the TbCo/Co interface becomes uniaxial for TA>100 °C. Even though the unidirectional character was not recovered by any field/anneal treatment, uniaxial anisotropy above 120 Oe is maintained for TA=260 °C. Devices were fabricated using a process with a maximum temperature of 180 °C. No MR loss is found during process in test structures at wafer level. A prototype 10-μm-track width spin valve tape head for QIC applications gave a maximum output of 2.3 mVpp at 20 kfci.