Read performance of GMR heads with in-stack longitudinal bias layer

Shielded GMR heads with an in-stack bias layer were designed, fabricated, and their read performance was measured. Since the bias layer and the free layer antiferromagnetically couple at the edge of the sensor, a closed magnetic flux structure (CFS) is formed. The results of micromagnetic simulation revealed that when an MnIr antiferromagnetic layer is used to pin the magnetization of the bias layer, the Ms⋅t of the bias layer normalized by that of the free layer should be between 1.2 and 1.5. Here Ms and t are the saturation magnetization and the thickness of the layer. The read waveform of the fabricated head was noise free and well biased. The obtained read sensitivity of the CFS head was four times higher than that of a conventional abutted junction head. Calculation revealed that the read sensitivity of the CFS head was almost five times higher than that of conventional heads when the magnetic track width was reduced to 100 nm. Thus, CFS heads show potential for high track density recording.