This paper describes the influence of the stripe height on the critical current density of the spin-torque (ST) noise in the TMR heads using the GHz range noise spectra in detail. The critical current density above which the non-thermal fluctuation noise originates from the ST slightly increases, linearly decreases, becomes minimum, and further keeps constant as the stripe height is reduced. This result means that no trend of jc appears for the stripe height. The average critical current density is approximately +4.70 ± 1.1 × 1011 A/m2, suggesting that the non-thermal fluctuation noise by the ST in the TMR head is independent of the stripe height and occurs at the current density of 1011 A/m 2. This result also suggests that this non-thermal fluctuation noise will become a serious problem for the HDD in the near future.
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