Sensing-current dependence of peak asymmetry in CPP-GMR heads

The read performance, especially peak asymmetry, of current-perpendicular-to-the-plane giant-magnetoresistive (CPP-GMR) heads with a current screen layer (nano oxide layer having a confined current path) was investigated through a spin stand test and a micromagnetic simulation. We fabricated CPP-GMR heads having a magnetoresistive (MR) ratio of 3%. The head-amplifier signal-to-noise ratio of the CPP-GMR heads with longitudinal media was 18-27 dB with a bandwidth of 200 MHz. The peak asymmetry of these heads has a complicated dependence on the sensing current. This complicated behavior can be explained in terms of the particular transfer curve for the CPP-GMR head. The transfer curve calculated from the micromagnetic simulation was "stair-like," having kinks caused by the current-induced field. Increasing the sensing current changes the positions of the kinks on the transfer curve. This stair-like transfer curve directly influences the peak asymmetry through the sensing current. Accordingly, the longitudinal bias field, sensor size, and current-induced biasing should be considered when controlling the peak asymmetry of the CPP-GMR heads.