Reiko Arai

Spin-valve heads utilizing antiferromagnetic NiO layers

Spin-valve heads utilizing antiferromagnetic NiO layers as the pinning layers were investigated. Advantages of using NiO are (1) superior corrosion resistance, (2) relatively high blocking temperature and (3) reduction in the heat generation due to current shunting. Spin-valve films of a structure of NiO/NiFe/Cu/NiFe show large /spl Delta//spl rho///spl rho/ (approximately 4%) and good sensitivity. Thin Co layers inserted between NiFe and Cu improve both /spl Delta//spl rho///spl rho/ and the thermal stability. To explore the feasibility of spin-valves with NiO, unshielded sensors with hard bias structure having longitudinally magnetized permanent magnets were fabricated. Irregular response in the transfer curves can be suppressed when the permanent magnet strength M/sub r/t is 0.5 memu/cm/sup 2/ or more. The linear response region of the spin-valve sensor was optimized by adjusting the thickness of the pinned layers and the sensor height. Finally, by incorporating these results a shielded spin-valve head with a track width of 2.4 /spl mu/m, a gap length of 0.3 /spl mu/m and a sensor height of 0.7 /spl mu/m was fabricated The response was noise-free and the output obtained with a small sense current of 0.41 mA was approximately 1 mVp-p, demonstrating a high sensitivity of a spin-valve head utilizing NiO.

Exchange-biased soft underlayers for perpendicular recording

We inserted NiFe/CoFe/antiferromagnetic-MnIr/CoFe layers between two CoTaZr soft layers to enhance the exchange-bias field (H/sub eb/) and then evaluated the effect of this lamination on the spike noise and recording characteristics of CoCrPt-SiOx media with an exchange-biased soft magnetic underlayer (SUL). The two CoTaZr layers were exchange-biased radially throughout the disk, and a higher H/sub eb/ was obtained for the upper CoTaZr layer. By using the laminated SUL, spike noise was suppressed even when the total thickness of the CoTaZr layers was increased to 300 nm. Although the medium had a high H/sub c/ of 7.0 kOe, a fairly good overwrite and signal-to-noise ratio were obtained. As another application of exchange biasing, we also examined the possibility of combining exchange biasing and antiparallel-coupled (APC) soft layers; i.e., a pinned APC SUL. An exchange-bias field from the pinning layers to the lower CoTaZr layer and an exchange-coupled field between the two CoTaZr layers were successfully applied. The medium with the pinned APC SUL showed no spike noise throughout the disk, and wide-area adjacent track erasure was effectively suppressed.

Spin-Valve Films Using Exchange-Coupled CrMnPt/Co Structure

Spin-valve films using CrMnPt/Co structure were investigated. The exchange coupling field (Hex) applied on 3 nm thick Co pinned layers was increased by annealing from 190 Oe to 320-380 Oe. The annealing treatment necessary for the enhancement of the Hex was typically 230/spl deg/C, 1 hr. The annealing distorted the crystal lattice of the CrMnPt films, which is likely to enhance the Hex. The blocking temperature was 320/spl deg/C. The resistivity of the CrMnPt films was as high as 300 /spl mu//spl Omega/cm resulting in low current shunting to antiferromagnetic layers in spin-valve films.

Effect of metallic additives (M) on the exchange coupling of antiferromagnetic CrMnMx films to a ferromagnetic Ni81Fe19 film

Among metal additives M(M:Pt, Pd, Rh, Ir, and Cu) of antiferromagnetic CrMnMx films, Pd was the most suitable M for obtaining large exchange coupling. For the 50 nm CrMnPd5/40 nm Ni81Fe19 films, the exchange coupling field of ∼28 Oe and the blocking temperature of ∼380 °C could be obtained. The CrMn(Pt, Pd, or Rh)x films having the optimum content of ∼8, ∼5, or ∼11 at.% exhibited the same high blocking temperature. The high blocking temperature of the CrMnPt8, CrMnPd5, and CrMnRh11 films was attributed to the nearest neighbor Mn–Mn within the respective films being at the same distance as that at which the Mn–Mn exchange integral showed the maximum negative value.

Current progress of single-pole-type GMR heads for perpendicular recording

We studied several proposals to address the problems encountered when single-pole-type giant magnetoresistive (SPT-GMR) heads are applied to an actual recording system. The first area of problems was regarding side erasure when there is a head skew. We fabricated a trapezoid-shaped main pole using a focus-ion-beam trimming or using a new wafer-processing technique and examined their write performances and their effects on reducing side erasure. The second area of problems concerned the stray field robustness of SPT-GMR heads when combined with a double-layered perpendicular recording medium. We tried to optimize the robustness and write performance by changing the width of a yoke in the main pole or by positioning a shield above the main pole. The stray field robustness and write performance were adequate in both cases, but a tradeoff relationship exists between both performances.

High frequency characteristics of multi-layered CoTaZr cores for thin film heads

Multilayered cores made of CoTaZr amorphous films with alumina interlayers were prepared and their high-frequency characteristics were investigated in order to develop magnetic thin-film heads applicable to higher transfer rate use. Compared with single-layered cores, head noise and relaxation noises decrease significantly in multilayered cores. Head noise decreases over 20% in the frequency region of 40 MHz, while relaxation noises are reduced gradually as the number of layers increases. These results are attributed to the reduction of eddy current and core losses due to wall motions. Accordingly, multilayered CoTaZr films are expected to be used to fabricate thin-film heads with low noise. >

Insulator thickness dependence of tunnel magnetoresistance effect in a model of Co/Al-oxide/Co junctions

The tunnel magnetoresistance (TMR) effect in Co/Al-oxide/Co junctions was studied on a model exhibiting positive spin polarization, in which an Al monolayer is regarded as the terminating layer of the ferromagnetic electrode, and the s electron of Al behaves as the tunnel electron. In this model, the TMR ratio decreases when an insulator becomes ultrathin. It was shown that the decrease originates from an increase in the self-energy corrections due to the electrodes with parallel magnetization configuration.

Wide band erasure caused by SUL domain wall in perpendicular recording media

The paper points out that soft magnetic underlayer (SUL) domain wall causes wide-band erasure in perpendicular recording media, and that laminated or multi-layered SUL can avoid this problem. Additionally, the spike noise produced by SUL causes bit error rate (BER) degradation. The types of SUL required to solve neighboring track erasure are similar to the approaches proposed to solve the spike noise problem. Thus, controlling the SUL domain is very important, not only for BER performance, but also for the reliability of the recorded information.

Effects of spike noise on read/write performance of double layered perpendicular media

In this paper, we analyzed the spike noise observed on media with FeTaC under layer generally have smaller amplitudes. Both amplitude and the amount of spike noise have been reduced by laminating the FeTaC underlayer.

Evaluation of Magnetization Process in Thin Film Head by Spin-Polarized SEM

The magnetic domain structures of NiFe films in thin film heads driven by dc and ac currents were investigated using spin-polarized SEM, in order to study the magnetization process under high-frequency magnetic fields. The image contrast under a high-frequency magnetic field was calculated as the time-averaged component of the magnetization along the detection direction due to magnetization rotation and to reversible domain wall movement. From the relation between the observed domain images and the calculated distribution of the average magnetization about the domain wall, it was found that irreversible domain wall movement occurs throughout the magnetic core under high-frequency excitations. Domain walls move slightly and reversibly until the direction of the magnetic field is reversed under high-frequency excitation.