Instability evaluation for permanent magnet biased magnetoresistive heads

We have used micromagnetic modeling to study instability of permanent magnet biased magnetoresistive heads. A new approach based on the dependence of reproducing characteristics on initial magnetization is proposed to examine the instability of both AMR and spin-valve heads. When the permanent magnet strength is smaller than a critical value, the output voltage of an AMR head depends on the initial magnetization, which results in instability. The critical permanent magnet strength gradually increases as shield-to-shield separation decreases. The critical value for spin-valve heads is smaller than that for AMR heads, because the pinned layer under a large exchange field does not change its magnetization at all