Nano-oxide Layer Research Articles

Nano-Oxide Layer Formed on Ruthenium of Synthetic Pinned-Structure Spin Valve by Ion Beam and Cluster Ion Beam Oxidation

In this paper, we report the performance of bottom synthetic spin-valve films with a newly developed ruthenium (Ru)-based nano-oxide layer (NOL). Two energetic oxidation techniques using an ion beam and a gas cluster ion beam were applied for the formation of the Ru NOL in the synthetic pinned layer. The giant magnetoresistance (GMR) was greatly enhanced from 13.8% to 15.7% with no sign of degradation in the pinning strength. In addition, these Ru NOL-bearing spin-valve films have demonstrated an excellent thermal stability, withstanding repeated thermal annealing cycles at elevated temperatures. This performance is clearly superior to that from the spin-valve films with a conventional CoFe-based NOL. The Ru NOL has shown a great potential for high-amplitude read sensor applications.

Oxygen-Mediated Mn Diffusion in Magnetic Tunnel Junctions Comprising a Nano-Oxide Layer

Mn diffusion toward the tunnel barrier in the hard layer system of a magnetic tunnel junction is recognized as the limitation for the temperature stability. In a series of experiments, a nano-oxide layer (NOL) was included into the hard layer as a diffusion barrier. The tunnel magnetoresistance (TMR) ratio has been monitored and interpreted as a function of anneal temperature, in combination with Auger analysis. At elevated anneal temperature, a more pronounced TMR decay was observed that originates in a different diffusion mechanism for Mn atoms, compared to tunnel junctions without NOL.

MR Ratio Enhancement by NOL Current-Confined-Path Structures in CPP Spin Valves

We have compared the magnetoresistance (MR) performance of current-confined-path (CCP) current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) spin valve films with a nano-oxide-layer (NOL), made between natural oxidation (NO) and ion-assisted oxidation (IAO). For the NO, an MR ratio was only 1.5% at an RA of 370 m/spl Omega//spl mu/m/sup 2/, whereas for the IAO, an MR ratio was greatly increased to 5.4% at an RA of 500 m/spl Omega//spl mu/m/sup 2/. Fitted data by the Valet-Fert model showing larger MR enhancement effect by the IAO is explained by the improvement of the metal-purity of the Cu inside the CCP structure. By further improvement of metal-purity of the Cu, a large MR ratio of more than 30% can be expected at a small RA of 300 m/spl Omega//spl mu/m/sup 2/. The CCP-CPP spin valve film is a promising candidate for realizing high-density recording heads for 200 to 400-Gbpsi recording.

Magnetism of Co<tex>$_1 - rm x$</tex>Fe<tex>$_rm x$</tex>-NOL in Specular Spin-Valves

We investigated the magnetic properties of the Co/sub 1-x/Fe/sub x/-natural oxidized nano-oxide layer (NOL) in the specular spin-valve system by precise measurement of magnetization at 77 K and M-T curves after field cooling at /spl plusmn/5 kOe. The result suggests the antiferromagnetic component behavior of the NOL and its Ne/spl acute/el temperature (T/sub N/) shifts to the higher temperature with increasing Fe composition. Below the T/sub N/, the antiparallel spin configuration at the pinned layers is stabilized by the exchange bias field induced from antiferromagnetic component of NOL by the field cooling in negative field direction.

Magnetoresistance and thermal stability enhancement in FeCr-based spin valves

In a synthetic spin valve (SV), a thin FeCr layer inserted in the pinned layer closer to the antiferromagnetic layer was found to improve the magnetoresistance, the pinning field strength, and thermal stability. Single SVs with 1-nm-thick FeCr inserted in the pinned layer shows a magnetoresistance ratio (MR) of 18% and a pinned field of about 1700Oe. This letter reports on the high MR in an all-metal single SV without specular scattering using a nano-oxide layer or spin filtering. This result, suggests that FeCr with high resistance and low spin polarization is effective in increasing the spin scattering and maximize the contribution of the pinned layer closer to spacer on the magnetotransport while keeping its antiferromagnetic exchange coupling high. The FeCr thin layer may also have an effect on minimizing Mn diffusion into the pinned layer and spacer as revealed by the increase of the pinning field.

Interface or bulk scattering in the semiclassical theory for spin valves

By taking into account spin asymmetries of the interface transmissions and the bulk mean free paths, we have treated pure interface, non-pure interface, bulk, and interface plus bulk scattering within the semiclassical Boltzmann theory. First, the optimizations of NOL (nano-oxide-layers) insertions in bottom, synthetic, and dual spin valves and the variations of the giant magnetoresistance (GMR) with the thickness of the free layer have been examined. For non-pure interface, bulk, and interface plus bulk scattering, qualitative trends of GMR versus NOL positions in spin valves are similar to each other. For pure interface scattering, there is no optimized NOL insertion positions and the blocking effect of the NOL inserted in the spacer remains effective as other three kinds of scattering. The GMR ratio for bulk scattering simply approaches zero when the free layer thickness becomes short; in contrast, for interface scattering or interface plus bulk scattering, the GMR ratio is nonzero at zero thickness of the free layer. Second, the relationships between GMR and specular and diffusive scattering have been explored. As far as specular reflection is concerned, our results imply that for a realistic bottom spin filter spin valve, Ta/NiFe/IrMn/CoFe/Cu/CoFe/Cu/Ta, roughness of the surfaces of Ta and the interfaces of Ta/NiFe, NiFe/IrMn, pinned layer/spacer, and spacer/free layer may lead to large GMR. We also find that the enhancement of GMR due to surface specular reflection is only a pure interface effect. The dependences of GMR on the specular transmissions roughly follow square relations. The trends of GMR against the spin-down diffusive scattering depend on the values of the spin-up transmission. Finally, impurity scattering was investigated and our semiclassical results are in qualitative agreement with the experiments and the quantum theory.

Thermally stable MnIr based spin valve type tunnel junction with nano-oxide layer over 400 °C

We have investigated the annealing effect of magnetic tunnel junctions (MTJs) with or without nano-oxide layer (NOL). For MTJ without NOL, TMR ratio increased up to 300 °C and the highest value was 21.6%. On the other hand, TMR ratio of MTJ with NOL increased up to 400 °C and the highest value was 22.7%. As shown in the auger electron spectroscopy (AES) and transmission electron microscopy (TEM) results, this improved thermal stability is due to NOL in the pinned layer. Mn diffusion into Al–O barrier is blocked and interface of Al–O is smothered by NOL. These may be the main reasons of high thermal stability of MTJ with NOL.

Improved thermal stability of Mn-Ir-based magnetic tunnel junction with nano-oxide layer

Si/SiO 2 /Ta/NiFe/Mn-Ir/CoFe/NOL/CoFe/Al-O/CoFe/NiFe/Ta bottom conventional (without nano-oxide layer, NOL) and specular (with NOL) MTJs were prepared by DC magnetron sputtering methods. In the case of a conventional MTJ, the TMR ratio increased up to 300 °C but the TMR ratio of a specular MTJ increased up to 400 °C. The highest TMR ratios of two samples after annealing at each optimal temperature were 21.6% (conventional MTJ) and 22.7% (specular MTJ), respectively, This improved thermal property of the specular MTJ is due to the NOL, which could act as a diffusion barrier for Mn. The bias-voltage dependence of both samples was vastly improved after annealing at each optimal temperature.

Thermal stability and specular reflection behaviour of CoNbZr-based bottom spin valves with nano-oxide layer

The thermal stability and specularity aspects of a CoNbZr-based bottom spin valve (SV) employing a nano-oxide layer (NOL) were investigated. The magnetoresistance (MR) ratio of the as-deposited CoNbZr-based bottom SV increased by 62% (from 6.3 to 10.2%) with incorporation of the NOL. The enhancement of the MR ratio was considered to be due to the specular effect (Δρ increased from 0.722 to 1.363 μΩ cm) of the NOL. The MR ratio of a Ta-based bottom SV decreased by about 45% (from 6.9 to 3.8%) when the samples were annealed at 300 °C for 240 min. By contrast, the MR ratio of the CoNbZr-based bottom SV with NOL increase d by 14 % (from 10.2 to 11.7%). The root mean square roughness value of the CoNbZr layer (0.07 nm) was superior to that of the Ta layer (0.43 nm). Although Mn in IrMn diffused out to the surface through the active layers resulting in the formation of Mn oxide at the surface in the CoNbZr-based bottom SV, no trace of Mn was found in the active layers and no significant degradation occurred. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Magnetoresistance of antiferromagnetic Ir22Mn78-pinned spin filter specular spin valves

Specular spin valves (SSVs) having the spin filter layer (SFL) in contact with the ultrathin free layer of composition Ta3/NiFe2/IrMn7/CoFe1/(NOL1)/CoFe2/Cu1.8/CoFe(tF)/Cu(tSF)/(NOL2)/Ta3.5 (in nm) deposited by magnetron sputtering were studied. For these antiferromagnetic Ir22Mn78-pinned spin filter specular spin valve (SFSSV) films, an optimal magnetoresistance (MR) ratio of 11.9% was obtained when both the free layer thickness (tF) and the SFL thickness (tSF) were 1.5 nm, and a MR ratio higher than 11% was maintained even when tF was reduced to 1.0 nm. This was due to an increase of specular electrons by the nano-oxide layer (NOL) and of current shunting through the SFL. Moreover, the interlayer coupling field (Hint) between the free layer and pinned layer could be explained by considering the RKKY and magnetostatic coupling. The coercivity of the free layer (Hcf) was significantly reduced as compared to traditional spin valves (TSV), and remained as low as 4 Oe when tF varied from 1 to 4 nm. It was found that the SFL made it possible to reduce the free layer thickness and enhance the MR ratio without degrading the soft magnetic property of the free layer. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Microstructure and magnetic properties of Mn–Ir based specular spin valve multilayer with nano oxide layer

Si/Ta/Ni–Fe/Mn–Ir/Co–Fe/NOL/Co–Fe/Cu/Co–Fe/Ta bottom specular spin valves were prepared by dc magnetron sputtering method. Under optimal oxidation conditions, the magnetoresistance ratio (MR ratio) and the H ex (exchange bias field) increased from 7.8% and 247 Oe without nano oxide layer (NOL) to 10.3% and 320 Oe with NOL, respectively. And the H in (interlayer coupling field) decreased from 35 to 19 Oe. These results indicate that NOL in the Co–Fe pinned layer improves the magnetic and electrical properties of spin valve. The NOL is formed discontinuously and this thickness range is about 0.5–2 nm. The chemical analysis shows that Fe-oxide is formed preferentially in the NOL.

Spin transfer effect in spin-valve pillars for current-perpendicular-to-plane magnetoresistive heads (invited)

Large spin-transfer effects were observed in spin-valve pillars developed for current-perpendicular-to-plane (CPP) magnetoresistive heads. The investigated samples are complex stacks including laminated free, synthetic/laminated pinned, and nano-oxide layers. The magnetoresistive (MR) transfer curves exhibit current-dependent loop shift and in some particular ranges of current and field, very large noise associated either to stochastic jump of the free layer magnetization or to excitations of steady precessional modes. A very unusual phenomenon of inverted coercivity was observed in the low current range. The spin-transfer effects show an asymmetry as a function of current direction. These experimental results indicate that the spin-transfer effects must be considered in the design of CPP MR heads.

Origin of Thermal Stability of IrMn Based Specular Spin Valve Type GMR Multilayer

By using the sputtering process, we made the IrMn based specular spin valve system, whose nano-oxide layer (NOL) was formed by natural oxidation. After thermal annealing at 305 and 410 °C, the thermal stability of the specular spin valve was observed. We found that the highest magnetoresistance (MR) ratio of about 12 % MR was produced after optimum annealing at 305 °C but the sample annealed at 410 °C also had a high MR ratio about 10 %. It is superior to other studies at this temperature. Based on the AES and XPS results, we could conclude that this enhanced thermal stability was due to the stable Cu layer between the pinned layer and free layer and to the NOL as a diffusion barrier for the Mn.

산화층 삽입에 따른 NiO/Co/Cu/Co 스핀밸브 박막의 열처리에 의한 자기적 특성

Magnetic properties are investigated for spin valves of Si/SiO/Ta(3 nm)/NiO(60 nm)/Co(2.5 nm)/Cu(1.95 nm)/Co(4.5 nm)/NOL(t nm ; Nano Oxide layer)/Ta(3 nm) with annealing. The annealing effect of spin valves with NOL are shown larger MR ratios from 10% to 12%. However lower enhancement of MR ratios. The spin-valves with NOL also showed almost constant R and smaller R. Enhanced MR ratios of spin valves with NOL after annealing result mainly from small values of R with constant R which due to specular diffusive electron scattering at NOL(NiO)/metal interfaces.ጊ☀Ѐ㘵㠻Ԁ䭃䑎䷙᜖එ6㔸⸰㔻Ԁ䭃䑎䷁ਖ਼3㌰㬅K䍄乍

Impact of the magnetism of nano-oxide layers on the GMR effect in specular spin valves

Abstract We study the magnetic effects of the nano-oxide layers of specular spin valves, based on zero-field-cooling and field-cooling (under H = H 0 ) experiments in the 320–15 K temperature range. One finds a small increase (decrease) of Δ R / R at 15 K after H 0 >0 ( R / R minimum occurs when H 0 =−500 Oe. Also Δ R / R ( T , H 0 ) departs from the ZFC curve at T ≈175 K. These features are related to magnetic ordering in the oxide layers.

Influence of nano-oxide layers on IrMn pinned bottom spin-valves at different positions

Abstract The influence of nano-oxide layer (NOL) inserted at different positions on interlayer coupling ( H in ), coercivity of free layer ( H cf ), exchange bias ( H ex ) and MR ratio of IrMn pinned bottom type spin-valves (SV) were studied. Weak antiferromagnetic interlayer coupling was observed in NOL-added SV. The NOL inside pinned layer and after free layer can enhance the MR ratio remarkably. MR of SV with a structure Ta3/NiFe2/IrMn6/CoFe1/NOL/CoFe2.3/Cu2.2/CoFe2.3/AlO reached 18.2%. This is one of the best values ever reported for all-metal single spin-valves.

Effect of nano oxide layer on exchange bias and GMR in Mn–Ir–Pt based spin valve

Abstract We have investigated the effect of nano oxide layers (NOLs), which were fabricated by a plasma oxidation of CoFe layer on the magnetic properties and magneto-resistance (MR) in a Mn–Ir–Pt based spin valve. The adjusted NOL could result in the high MR and the strong exchange coupling field ( H ex ). From a high resolution electron microscopy analysis the oxide was about 1 nm. The strong reflectivity at the interface of a free and oxide capping layer should lead to the decrease of an interlayer coupling field, which could possibly improve the H ex .

Enhancement of magnetoresistance in spin valves with ion sputtered Si substrates

The pattern of dots with height about 1.2 nm is formed on Si substrates by ion sputtering. Top, bottom spin valves, and bottom spin valves with a nano-oxide layer are fabricated on both non-ion sputtered and ion sputtered Si substrates. Magnetoresistance ratio increase around 10% has been achieved in the spin valves on the ion sputtered substrates.

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/.

Thermal and Mn diffusion behaviors of CoNbZr-based spin valves with nano oxide layers

The authors investigated the specularity and thermal characteristics of CoNbZr-based spin valves (SVs) with and without employing nano oxide layers (NOL). Both CoNbZr- and Ta-based SV films composed of Si-SiO/sub 2/-CoNbZr (or Ta)-CoFe-NOL-CoFe-Cu-CoFe-IrMn-CoNbZr (or Ta) were prepared by rf magnetron sputtering. Magnetoresistance (MR) ratios in the as-deposited state increased 48% (3.4% /spl rarr/ 5.0%) with incorporation of NOL. In particular, a remarkable enhancement (about 95%) in the MR ratio after annealing at 300/spl deg/C for 20 min was observed (5.0% /spl rarr/ 9.8%). According to the Auger electron spectroscopy depth profile, the large increase of the MR ratios in the initial stage of annealing were due to the double specular scattering effects by the Mn-oxides at the surface and the NOL in the free layer. Due to high affinity of Mn for oxygen, Mn diffused preferentially to the position of high oxygen potential (such as the surface or the NOL) during prolonged annealing. The authors could artificially control the diffusion direction of Mn by providing an oxygen potential (like inserting NOL) in the SV structure.