Extra-low-frequency noise in giant magnetoresistance recording heads

Extra-low-frequency (ELF) noise was studied in flyable, shielded giant magnetoresistance heads using a novel, ultralow-noise amplification system. The noise power spectral density had a 1/f character over wide frequency and sense current ranges. The noise was mainly magnetic in origin. It, however, did not follow Hooge's formula. Random telegraph noise (RTN) was observed after moderate current stressing. The characteristic dwell times of the two-level RTN switching changed with applied field, sense current, and temperature. We consider the ELF noise as a sensitive diagnostic tool, since deviations from the 1/f dependence signal the existence of undesirable magnetic states. (C) 1999 American Institute of Physics. [S0021-8979(99)33008-5].