Analysis of Magnetic Fluctuations Noise due to a Pinned Layer

Abstract

Magnetic fluctuation noise due to a pinned layer (Nmag-pin) was measured to improve head-amp SNR by using fabricated heads, and the results were confirmed through micro-magnetic simulations. An experiment revealed that the Nmag-pin decreased as exchange coupling Jk and/or sensor aspect ratio (SH/Twr) increased. These results were consistent with the simulated ones. Reduced Nmag-pin was expected by both increasing Jk and larger SH/Twr. The simulations indicated that the head with Jk ~ 1.3 erg/cm 2 suppressed most Nmag-pin, and demonstrated improved head-amp SNR around 1 dB.

Read-head Conditions for Obtaining Areal Recording Density of 5.8 Tbit/in.2 on a Bit-Patterned Medium

“…The curve for ÁSNR headðTWR25!15nmÞ of 13 dB is estimated from experimental head noise. 24) It is assumed that when head noises are one third and one half of the noise in the case that ÁSNR headðTWR25!15nmÞ is 13 dB, the decreases of ÁSNR head are 7 and 9 dB.…”

“…Head noise (namely, electronic noise and thermal magnetic-fluctuation noise), however, becomes large as TWR is decreased, because electrical resistance of the read head increases and volume of the magnetic layer of the MR head decreases. [24][25][26] Besides, medium noise of a BPM is expected to be low because of low transition noise. Accordingly, head noise might be the key factor in obtaining the optimum conditions for designing an MR head.…”