CPP-GMR with oxidized CoFe layer on various lower-electrode materials

We investigated current perpendicular to the plane-giant magnetoresistive (CPP-GMR) films with a current screen layer of oxidized CoFe. The magnetoresistance (MR) ratio increased monotonically with an increment of resistance-area product (RA) when the thickness of the precursor CoFe layer was increased. We were able to obtain a high MR ratio of 6.7% at an RA of about 2 Ωμm². Based on transmission electron microscopic observations, the current screen layer was crystalline, and some metal portions were locally observed in the current screen layer. We also investigated the dependence of CPP-GMR properties on he crystalline structure by changing lower-electrode materials. Decreasing RA without a degradation of MR ratio was observed with increasing grain sizes by changing the lower-electrode materials. Fabricated read heads for perpendicular recording, which had a track-width of 80 nm with an MR ratio of 3% and an RA of 0.6 Ωμm², showed a high output voltage of 2.2 mV and a good head-amp signal-to-noise ratio of 30 dB, at an operating voltage of 120 mV. Therefore, an improved CPP-GMR film up to a high MR ratio of 6% at the low RA of 0.3 Ωμm² with good soft magnetic properties is promising for future read heads of over 200 Gb/in².