Seiji Kumagai

Longitudinal bias method using a long distance exchange coupling field in tunnel magnetoresistance junctions

A longitudinal bias method using a long distance exchange coupling field, which was observed between an IrMn layer and a NiFe/CoFe bilayer across a Cu interlayer, has been investigated for magnetic read heads. The exchange coupling field could be changed in the layered film consisting of Ta/NiFe/Cu(0, 1.0, 1.5, 2.0 nm)/IrMn. In order to align the easy axes of the free and pinned ferromagnetic layers perpendicular to each other, a two-step annealing process was carried out to rotate the easy axis of the free layer in the tunnel magnetoresistive read heads. The angle between the two easy axes was 72° in the junction after an optimized two-step annealing. The tunnel magnetoresistive readers, which have a resistance×area product of about 2000 Ωu200aμm2 and a tunnel magnetoresistance ratio of about 15%, showed an output voltage of 9080u200aμVp−p and 2270u200aμVp−p/μm, which was comparable to that of a typical giant magnetoresistive reader for a 7.5 Gbits/in.2 hard disk drive.

Magnetoresistance of Co/sub 100-x/Fe/sub x//Al-oxide/Co/sub 100-x/Fe/sub x/ tunnel junctions

The relationship among Co/sub 100-x/Fe/sub x//Al-oxide/Co/sub 100-x/Fe/sub x/ tunnel junctions (x=0, 10, 25, 40 and 50) and tunneling magnetoresistance (MR) was investigated. The highest MR ratio of 40.7% was observed for Co/sub 75/Fe/sub 24//Al-oxide/Co/sub 75/Fe/sub 25/ junctions. The MR ratios for Co/sub 75/Fe/sub 24//Al-oxide/Co/sub 75/Fe/sub 25/ junctions were almost constant as a function of junction area, which implies that those junctions that possess the MR ratios over 40% do not show geometrical enhancement effect on the MR ratios. After annealing at 200/spl deg/C, MR ratio of 49% was obtained for the Co/sub 75/Fe/sub 24//Al-oxide/Co/sub 75/Fe/sub 25/ junctions. When the bias voltage was between 360 and 455 mV, the MR ratio decreased to half its value at 1 mV. MR ratio was observed over 20% at 400 mV For Co/sub 75/Fe/sub 25//Al-oxide/Co/sub 75/Fe/sub 25/ junctions. The bias voltage dependence of MR ratio was related to the barrier height of the junctions. MR ratio decreased more slowly with increasing bias voltage for those junctions with high barrier heights.

Flux guide type tunnel-valve head for tape storage applications

The feasibility of tunnel magnetoresistive read heads with flux-guide (FG) layers was investigated for helical-scan tape storage applications. In order to stabilize tunnel-valve elements, a long-range exchange coupling bias scheme was employed, consisting of a Cu layer and an antiferromagnet deposited on top of a free layer in the tunnel-valve element. The maximum output of the FG type reader was about four times larger than that of a conventional anisotropic magnetoresistive reader, and thermal asperity noise of the magnetoresistance reader could be reduced drastically. The tunnel-valve readers have symmetrical track profiles, which are suitable for nontracking tape systems.

Flux-guide type tunnel-valve head for helical scan tape system

Summary form only given. In helical scan tape drives, wearing of the reader on the drum that rotates at high speed gives rise to the deterioration of reliability. In order to achieve high reliability and high density recording, flux-guide (FG) type MR readers using magnetic tunnel junctions were fabricated for the tape drives. A longitudinal biasing scheme, which combines permanent magnet biasing with a long-range exchange coupling biasing toward all the track positions (E. Nakashio et al, J. Appl. Phys. vol. 89, p. 7356, 2001), was utilized to stabilize the FG type tunnel-valve readers.