Yutaka Shimizu

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/.

Top, bottom, and dual spin valve recording heads with PdPtMn antiferromagnets

We fabricated top-type (Substrate/free layer/Cu/pinned layer/antiferromagnetic layer) and bottom-type (Sub./antiferro/pinned/Cu/free) spin valve heads using PdPtMn antiferromagnets. Bottom type spin valve head with a buffer layer of Ta/NiFe showed similar exchange bias field and MR ratio as top-type spin valve head. Dual spin valve (DSV) films with two pinning layers of PdPtMn had an enhanced MR ratio by 40% compared to the top-type spin valve. Patterned DSV elements with 3 /spl mu/m MR height showed relatively large deviation from the optimum bias state. In order to adjust the bias point, asymmetric DSV elements with Cu layers of different thicknesses were investigated. Asymmetric DSV with the structure of Ta/NiFe/PdPtMn/CoFe/Cu(t/sub 1/)/CoFe/NiPe/CoFe/Cu(t/sub 2/)/CoFe/PdPtMn (t/sub 1//spl ne/t/sub 2/) showed an improvement for just bias using sense current magnetic field. The possibility of reducing the PdPtMn critical thickness for exchange coupling was investigated using ultra high vacuum (UHV) deposition environment. UHV technique is significantly useful to obtain exchange bias field (H/sub ua/) of PdPtMn(t)/ferro at t 500 Oe), large sheet resistance change (/spl Delta//spl rho///sub total/=1.6 /spl Omega/), and good thermal stability up to 300/spl deg/C. The total thickness of DSV was also reduced from 80 to 53 nm. Single and dual spin valves with thin PdPtMn pinning layer are very promising sensors for ultra high density recording applications.

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.

Dual Spin-valve with Pd-Pt-Mn Anti-ferromagnetic Layer

The exchange bias field (H/sub ex/) between a new antiferromagnetic film of Pd-Pt-Mn and a soft magnetic layer was investigated with stacked structures having a Pd-Pt-Mn layer both on and under the soft layers. Pd-Pt-Mn on a Ta/Ni-Fe bilayer buffer exhibits high orientation and a large H/sub ex/ to a soft layer deposited on the Pd-Pt-Mn. Using this Ta/Ni-Fe buffer layer, dual spin-valve films with Pd-Pt-Mn antiferromagnetic layers were fabricated. After a 230/spl deg/C anneal to order the Pd-Pt-Mn, the MR ratio reaches 9.2% and the H/sub ex/ of the dual spin-valve is about 255 Oe, which is high enough to provide spin-valve operation.

The temperature dependence of exchange anisotropy in ferromagnetic/PdPtMn bilayers

We have studied the differences in the temperature dependence of exchange anisotropy of PdPtMn/CoFeB, NiFe, and NiFeTa bilayers to understand the role of ordering temperatures. The three different ferromagnetic layers [Curie temperatures: TCNiFeTa(400 °C)<TCNiFe(570 °C)<TCCoFeB(1040 °C)] exchange biased by the same antiferromagnet [Neel temperature: TNPdPtMn(600 °C)] showed significantly different behavior: the exchange bias field was monotonically decreasing with temperature for the CoFeB and showed distinct, broad peak for NiFe and NiFeTa at a lower temperature before it decreased above 200 °C. The temperature dependence of exchange anisotropy, calculated from the measured exchange bias field and saturation magnetization, was also different for the three bilayers as a result of the differences in Hua and MFM. The results could be understood by the modified thermal fluctuation aftereffect model, which includes the temperature dependence of the ferromagnetic magnetization and the assumption that the order...

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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We have succeeded in enhancing the current-perpendicular-to-plane (CPP) magnetoresistance of the synthetic spin-valves by controlling the spin-dependent transport through the synthetic ferrimagnetic pinned layer using impurities. The new pinned layer overcomes the disadvantage of the synthetic pinned layer in CPP spin-valves for the magnetoresistance reduction. The experimental results are well described by our calculations based on the two-current theory. The proposed pinned layer, together with our newly developed magnetoresistive ferromagnetic materials, will be quite effective in producing CPP spin-valve sensors for ultrahigh-density data storage systems.

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

In this article, we introduce a novel Co‐rich Co‐Ag/Cu granular alloy structure with increased magnetic sensitivity, and report on our study of the relationship of giant magnetoresistance (GMR) and magnetic properties to annealing temperature and Cu thickness in sputtered Co66‐Ag34/Cu multilayered films. We heat treated Co‐Ag/Cu films with Cu spacer thickness ranging from 15 to 50 A up to 500 °C, and found that the MR ratio loosely depends on both the Cu spacer thickness and the annealing temperature, peaking at 7.6% with a 25 A Cu layer and an annealing temperature of 280 °C. Based on the magnetic properties we observed, as well as x‐ray studies, we found that Cu spacers at least 25 A thick are able to separate the Co‐Ag magnetic layers. Our data also indicated that the annealing treatment changed the coupling of magnetic layers from ferromagnetic to antiferromagnetic. The high thermal stability and the high magnetic sensitivity suggest potential use of our novel multilayered structure in applications as...