Yoshihiko Seyama

Giant magnetroresistance properties of specular spin valve films in a current perpendicular to plane structure

Conventional and specular spin valve films in a current perpendicular to plane (CPP) structure have been investigated. The specular spin valve film with bottom type structure had two oxidized layers: one in the pinned layer, which was oxidized during an in situ deposition process, and the other in the free layer, which was a naturally oxidized Cu/Ta cap. Both films had increasing resistance, R, and resistance change, ΔR, with decreasing element size. The conventional spin valve film showed a resistance times area product, RA, of 144 mΩ μm2 and a resistance change area product, ΔRA, of 0.7 mΩ μm2 while the specular spin valve film showed RA of 1120 mΩ μm2 and ΔRA of 23 mΩ μm2. The ΔRA of the specular spin valve film was about 33 times larger than that of the conventional spin valve film. The calculated magnetoresistance (MR) ratios, MRSV, of each spin valve film were 1.9% and 2.3%, respectively. We think oxidized layers in the spin valve film caused the specular electron scattering and this lengthened the ...

Spin-valve heads in the current-perpendicular-to-plane mode for ultrahigh-density. recording

We have investigated the magnetoresistance properties of spin valves in the current-perpendicular-to-plane (CPP) mode. Conventional single spin-valve (SV) film shows resistance area product RA=81 m/spl Omega//spl mu/m/sup 2/, and resistance change area product /spl Delta/RA=0.35 m/spl Omega//spl mu/m/sup 2/. For a CPP element of a single SV with oxide layers, /spl Delta/RA dramatically increased to 9.0 m/spl Omega//spl mu/m/sup 2/. Micromagnetics simulation revealed that the readback performance of the CPP head with low-impedance conventional SV film was much affected by sense current. On the other hand, the medium impedance CPP head, such as the SV film with oxide layers, shows several advantages compared with the low impedance head, such as higher output voltage, less influence by magnetic field of the sense current, and narrower core width.

Readout performance of confined-current-path current-perpendicular-to-plane heads

Current-perpendicular-to-plane (CPP) spin valve (SV) films with nano-oxide layers have been developed. The enhancement of giant magnetoresistance by inserting the current confining layer between free and pinned layers was confirmed by the calculation of the current-flow distribution using a finite-element model. For the bottom-type spin valve films with the structure of PdPtMn/CoFeB/Ru/CoFeB/Cu/oxidized CoFeB(t nm)/Cu/CoFeB, MR ratio of 5.0% and RA of 0.6 /spl Omega//spl middot//spl mu/m/sup 2/ were obtained at t=1.2 nm. The merged head using the CPP-SV film with a nano-oxide layer whose MR ratio was 3.2% was fabricated. The magnetic read core width was 130 nm when the physical free-layer width was 100 nm. 0.91 mV/sub p-p/ output voltage was obtained at the sense current of 4.8 mA which corresponds to the average current density of 19 MA/cm/sup 2/.

Perpendicular giant magnetoresistance of CoFeB/Cu single and dual spin-valve films

We present giant magnetoresistance measurements in the current-perpendicular-to-plane mode on single and dual spin valves whose areas are from 0.1 to 1.0 μm2. Dependence on the magnetic layer thickness and the structure was investigated. It was revealed that magnetoresistance change increases 20% by insertion of a nonmagnetic spacer layer in the free layer. The results were analyzed within the framework of the two-current series-resistor model, and proved to be consistent with the theory.

Giant magnetoresistance properties of CoFe/Cu multilayer in the CPP (Current Perpendicular to the Plane) geometry

The MR ratio of multilayer GMR sensors with the CPP (current perpendicular to the plane) structure is expected to be much larger than that of CIP (current in the plane) sensors. We investigated the GMR properties of CIP and CPP elements of a Co/sub 0.9/Fe/sub 0.1//Cu 10-bilayer. For CPP elements, the GMR film was connected to the top and bottom terminal layers with a micron-sized contact hole. The measured data was analyzed using a model taking into account of the distribution of sense current. The measured resistance change (l R) increased rapidly as the GMR diameter became smaller, and showed close agreement with the calculated results when we assumed the MR ratio of CPP films to be around 30%. This MR ratio was twice as large as that of the CIP film of Co/sub 0.9/Fe/sub 0.1//Cu 10-bilayer. In this study, we used the CPP elements which had wide GMR films and fine contact holes. So, the measured saturation field (/sub H/s) of the CPP elements was almost constant as a function of the contact hole dimension, because the demagnetization field was insensitive to the sensor size. The CPP element in this study will obtain a high output when the GMR diameter becomes small.

A Co-SiO

We have investigated a possibility of Co-SiO2 granular material as a current-confining layer of confined current path (CCP) type-current perpendicular-to-plane (CPP) spin valves (SVs). A resistance-area (RA) product can be controlled by a composition and a thickness of the Co-SiO2 granular layer, and it showed a higher controllability compared to a conventional oxidized metal current-confining layer. The CPP-SV with Co-SiO2 granular layer performed at a relatively large MR ratio of 5.7% with a RA of 1 Omegamum2 and showed a potential of 5% with 500 mOmegamum2. This indicates a role of the Co-SiO2 granular layer as a current-confining structure. Although a tolerance to an applied voltage is insufficient at this stage, a granular material as a current-confining layer, such as Co-SiO2 , will open a door to a realization of CPP-SV magnetic recording heads for an ultrahigh-density recording systemIt was confirmed that the confined current paths spin valves (CPP-SVs) employing the Co-SiO2 granular layer as the current confining layer show relatively large magnetoresistance (MR) ratio with higher controllerability compared to those with the conventional oxidized metal layer. We expect that the granular type current confining layer makes artificial fabrication of the CCP-CPP structure possible.

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Oxide vertical-cavity surface-emitting lasers (VCSELs) are widely used in high-speed fiber optical communications. Burn-in tests are run on oxide VCSELs to weed out defective devices, thereby fulfilling the related reliability requirements. Nevertheless, some oxide VCSELs fail in the field. Oxide VCSELs that failed in the field were examined with transmission electron microscopy (TEM). Besides cross-sectional views, plan views of the entire active region were observed. Development of a dislocation network in the active region was found in all samples, and that is the cause of the failures. The Burgers vectors of these dislocations are parallel to [101]. Although the trigger of the dislocations has not been identified, electrostatic discharge (ESD) does not cause the dislocation in our investigated devices, since no ESD-damaged region was found. Strain and/or crystal defects introduced during VCSEL fabrication are considered to be the cause.

Granular Material as a New Current-Confining Layer for Current Perpendicular-to-Plane Spin Valves

Summary form only given. Spin valves in the current-perpendicular-to-plane (CPP) mode, whose output voltage increases as the element size decreases, are the promising candidates for over 100 Gbit/inch/sup 2/ read heads. We have already verified an increase in the output by insertion of the nano-oxide layer (NOL) in the single-type spin valves (SSV) for the CPP elements (K. Nagasaka et al, J. Appl. Phys., vol. 89, p. 6943, 2001). It may be because sense current flows in the narrow regions due to the inhomogeneity of the NOL, which makes the effective element size smaller. In this paper, we examine the NOL insertion in the dual-type spin valves (DSV) that yield larger output when applied to the CPP elements than the SSV due to increment of the interfaces between magnetic and non-magnetic layers.