Search

The electric control of magnetic anisotropy has important applications for nonvolatile memory and information processing. By first-principles calculations, we show a large nonvolatile control of magnetic anisotropy in the ferromagnetic/ferroelectric CoPt/ZnO interface. Using the switched electric polarization of ZnO, the density-of-states and magnetic anisotropy at the CoPt surface show a large change. Due to a strong Co/Pt orbitals hybridization and a large spin-orbit coupling, a large control of magnetic anisotropy was found. We experimentally measured the change of effective anisotropy by tunneling resistance measurements in CoPt/Mg-doped ZnO/Co junctions. Additionally, we corroborate the origin of the control of magnetic anisotropy by observations on tunneling anisotropic magnetoresistance.

Recently, yttrium iron garnet (YIG, Y3Fe5O12) has been proved to be an efficient material for magnonics and spintronics application after discovery of spin pumping [1], spin seebeck effect [2] and spin hall magnetoresistance [3] phenomena.

We studied the formation mechanism of ferromagnetic nanocontacts (NCs) around 1-2 nm in diameter in thin AlOx nano-oxide layer (NOL) through in situ conductive atomic force microscopy (c-AFM), which is the only method suitable for measuring morphological changes in features this small. Spin valves (SVs) with Fe0.5Co0.5NCs in AlOx NOL fabricated by ion-assisted-oxidation (IAO) irradiated onto 1.3-nm-thick Al had nanocontact magnetoresistance (NCMR) characteristics with the MR ratio of 5% for 1 Ω μm2. According to measurements with c-AFM, these NCs were mostly located at the valleys between the AlOx grains or the edge of the grain. In other words, NCs were formed in the oxidation and cohesion process of Al by the IAO. Moreover, we found that the high-temperature annealing process improved the MR ratio to around 10% for 0.5 Ω μm2. The high-temperature annealing process may involve the AlOx morphological change and have led the Al atoms in NCs to migrate to AlOx by combining with oxygen as impurities. Then, the morphological changes and migration of Al caused NCs to be the low resistivity and the short length.

We confirmed the structural properties of trilayered epitaxial films with AML [Fe/Co]n and Au spacer on Au electrode by RHEED and TEM. A considerably large DeltaRA (2.61 mOmegamum2) resistance area product was observed in all metallic current perpendicular-to-plane giant magneto-resistance (CPP-GMR) spin-valve elements by using alternate monatomic epitaxial [Fe/Co]n ferromagnetic layer with IrMn layer on the top. The estimated spin scattering asymmetry coefficient beta and interface asymmetry coefficient gamma was 0.81 and 0.43 plusmn 0.05, respectively. This value of beta is higher than that of Fe50Co50/Cu laminated with Cu spacer or Heusler alloy which is largest value ever reported at room temperature.

We investigated the current induced magnetization dynamics, so called spin torque oscillation, in magnetic nano-contact MR element with a synthetic antiferromagnetic type spin-valve structure under high in-plane applied magnetic field of 0.9-1 kOe. Very high level oscillation of 18 nVHz-1/2 with narrow FWHM of 12 MHz was observed in the condition of negative applied current where electron-spin is injected from free layer to reference one. Applied current dependency on an oscillation frequency is a blueshift with good linearlity, and same dependency on level and FWHM is almost constant in the range of -10 to -14 mA, while applied field dependency on frequency shows redshift with two different slopes, -2.5 MHz/Oe in less than 1 kOe and -8.7 MHz/Oe in more than 1 kOe which field is smaller than the spin-flop field for the synthetic antiferromagnet, besides very clear and reasonable peak and bottom for oscillation level and FWHM are observed, respectively. It is thought that these magnetization dynamics are originated from synthetic antiferromagnet.

We investigated the influence of a direct current on domain wall magnetoresistance (DWMR) elements with Fe0.5Co0.5-AlOx nano-oxide-layer including ferromagnetic metal nanocontacts. The current induced microwave oscillation and changes in the shape of R-H curves with increase of sense current were observed. The origin of these results are considered to be spin transfer effect on the confined domain wall in ferromagnetic metal nanocontacts and current induced magnetic field adjacent to ferromagnetic metal nanocontacts because of high current density. Furthermore, our study indicates a high likelihood of correlation between microwave oscillation and R-H curves in high sense current. We infer current induce microwave oscillation in the higher resistance state which was observed after the jump of resistance by high sense current. Moreover, it is suggested that there is some correlation between oscillation frequency and degree of twist of magnetization in a domain wall.

Nano-contact magnetoresistance (NCMR) spin-valves (SVs) using an AlOx nano-oxide-layer (NOL) have numerous nanocontacts in the thin AlOx oxide layer. The NCMR theoretically depends on the bulk scattering spin asymmetry (β) of the ferromagnetic material in the nanocontacts. To determine the relationship between NCMR and β, we investigated the dependence of NCMR on the composition of the ferromagnetic material Co1−xFex. The samples were annealed at 270 °C and 380 °C to enhance the MR ratio. For both annealing temperatures, the magnetorsistance ratio in the low-resistance area product region at less than 1 Ω μm2 was maximized for Co0.5Fe0.5. To evaluate β exactly, we fabricated current-perpendicular-to-plane giant magnetoresistance SVs with Co1−xFex/Cu/Co1−xFex layers and used Valet and Fert's theory to solve the diffusion equation of the spin accumulation for a ferromagnetic layer/non-ferromagnetic layer of five layers with a finite diffusion length. The evaluated β for Co1−xFex was also maximized for Co0.5Fe0.5. Additionally, to determine the difference between the experimental MR ratio of NCMR SVs and the theoretical MR ratio, we fabricated Co0.5Fe0.5 with oxygen impurities and estimated the decrease in β with increasing oxygen impurity concentration. Our Co0.5Fe0.5 nano-contacts fabricated using ion-assisted oxidation may contain oxygen impurities, and the oxygen impurities might cause a decrease in β and the MR ratio.

In this paper, we mainly discuss the extendability of current perpendicular to plane giant magnetoresistive (CPP-GMR) heads beyond 100 Gbpsi by using micromagnetic simulation and simulation techniques. An area map of CPP-GMR's resistance-area product (RA) and magnetoresistive ratio for several areal densities is made, which suggests that downsizing of a CPP-GMR head does not cause a decrease in output voltage differently from a current in plane GMR (CIP-GMR) head. At this point, a CPP-GMR has the advantage of extendability to a higher areal density over CIP-GMR, and is the major candidate for the next generation. A CIP-GMR seems to have a scalability limit around 100-200 Gbpsi. On the other hand, the area map also suggests that the RA of the CPP-GMR is a more important keyfactor for higher areal density than for CIP-GMR. The CPP-GMR, therefore, requires not only higher MR, but also less RA as areal density gets higher. Tunneling MR (TMR) has exactly the same problem, so CPP-GMR also has many advantages over TMR, with too high an RA. Additionally, we present CPP-GMR films with the potential for around 500 Gbpsi and discuss a suitable read-head structure for CPP-GMR. Micromagnetic simulation results indicate that the read track width will be controlled by a magnetic field due to the sense current of CPP. We will discuss overall studies on scalability of CPP-GMR.

We investigated the microwave oscillations induced by spin transfer torque with a current-perpendicular-to-plane (CPP) nanocontacts spin-valve (NCSV) structure under dc current. First, we carefully studied the influence of the stress current, at which a synthetic-antiferromagnet (SAF)-spin-flop might take place with Joule heating under the applied field for measurement, on the SAF magnetization state for CPP-NCSV with high magnetoresistance (MR) ratio of approximately 20% to determine the applied current densities of the devices for microwave oscillation measurement, and then its microwave oscillation characteristics were clarified. The clear decrease in the MR ratio due to Joule heating was observed only in NCSV devices with high MR ratios. Therefore, the critical current density of the device for the microwave oscillation decreases with an increase in the MR ratio, which improves the oscillation efficiency. It suggests that the current is more effectively confined at NCs compared with the low MR devices. As a result, we succeeded in observing excellent oscillation characteristics, i.e., a large oscillation power of 64 nW and a narrow line width of 6.5 MHz at approximately 1.1 GHz in an NCSV device.

The concept of spin-filter spin-valve (SFSV) films is reviewed. The dependence of the free layer structure on the spin-filter effect was investigated by using model films and two types of free layers were compared, a single CoFe layer and a conventional NiFe/Co free layer. At the same magnetic thickness of the free layer, the SFSV films with a CoFe free layer showed a larger magnetoresistance (MR) ratio than those with a NiFe/Co free layer. This is partly attributed to the thinner CoFe free layer thickness, which is due to the fact that the CoFe free layer has higher Bs than the NiFe/Co free layer. Moreover, SFSV films with a CoFe free layer still showed a larger MR ratio when the free layer thickness was the same. It suggests that other factors contribute to the high MR performance, such as the quality of the interface between a free layer and a high conductance layer. Film performance of MR 9% to 10%, ΔRs 1.5–2.0 Ω, Hcea∼3 Oe, and λs⩽±0.5 ppm was obtained with a single CoFe free layer and synthetic anti...

The insertion of a nano-oxide-layer (NOL) into a spin valve system is well known to be very effective in enhancing the magnetoresistance ratio at both of current-in-plane (CIP) and current-perpendicular-to-plane (CPP) geometries. Recently, a clear NOL pinning assist effect is reported to be observed in the low temperature range below ~150 K by using the magnetic field cooling method from room temperature (R.T.) in the Co0.9Fe0.1 pin-NOL, wherein the NaCl-type CoO-FeO antiferromagnetic component exists. In this paper, the NOL pinning assist effect in a specular spin valve system with (Co-Fe)/Cr pin-NOL is presented. An ultra-thin Cr layer deposit on the Co-Fe layer before oxidation leads to increase the exchange bias field still more with the increment of the blocking temperature (TB)of the (Co-Fe)-NOL biasing in the low temperature range below R.T. and to fully exploit the superior pinning properties of the metallic antiferromagnet (Ir-Mn) at R.T. in the Co-rich region. The effect of ultra-thin Cr layer on the NOL exchange bias is considered from the aspect of the complicated oxide formation and its magnetism.

We have achieved a magnetoresistance (MR) ratio of 7%-10% at a resistance area product (RA) of 0.5-1.5 Omegamum2 by ferromagnetic FeCo nanocontacts in Al nano-oxide-layer (NOL) with current-perpendicular-to-plane spin-valve (CPP-SV) structure. Conductive atomic-force-microscopy shows clear current-path regions of a few nanometers in size surrounded by the Al-NOL. The MR dependence on resistance area product (RA) is well explained by the current-confined-path model assuming that the spin-dependent scattering has an FeCo nanocontact origin, different from tunnel magnetoresistance (TMR). Resistance increases with increasing bias voltage, indicating joule heating by high-current density in nanocontacts, in contrast to TMR. The MR origin is mainly interpreted as spin-dependent scattering due to domain wall formed at ferromagnetic nanocontact

The B2 structure Fe50Co50 alloy is very attractive material as a large spin conductance asymmetry. In this study, we have tried to fabricate epitaxial Fe/Co superlattice with B2 structure. In order to investigate the relationship between the film structure and the substrate temperature, the films were prepared at different substrate temperature. The film structure of Fe/Co was evaluated by reflection high energy electron diffraction (RHEED). The in-plane lattice spacing gradually decreased to that of a bulk Fe50Co50 as increase in the number of layers. The B2 structure ordered phase of Fe/Co superlattice was successfully confirmed by RHEED and X-ray diffraction (XRD).

The exchange bias properties of the Co/sub 1-x/Fe/sub x/ natural-oxidized nano-oxide layer (NOL) in the specular spin valve system are investigated. The exchange bias energy (J/sub ex/) increased with the Fe content of the CoFe NOL. This result suggests that the enhancement of the pinning field/energy at room temperature was induced by the inserted NOL into the pinned layer. The enhancement of both the magnetoresistance ratio and the exchange bias field was realized by increasing the Fe content in the Co/sub 1-x/Fe/sub x/ NOL.

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.

Nano-Oxide Layers (NOL) have been introduced recently as a means to enhance the degree of specular scattering at the outer surfaces in a spin-valve, while still using metallic antiferromagnets such as PtMn or IrMn. A key requirement of the NOL layer in the pinned layer is to be able to provide strong ferromagnetic coupling between two ferromagnetic layers. In this paper, a quantitative study of the ferromagnetic interlayer coupling over the NOL-layer is presented. A Stoner-Wohlfarth model is developed to allow for quantitative analysis. The effect of different metal deposition methods (PVD or IBD), different pinning structures (PtMn and IrMn; simple and synthetic) and different oxidation methods on the coupling is compared.

Three different techniques, natural oxidation, remote plasma oxidation and low energy ion beam oxidation, have been proved to be equally effective in forming nano-oxide layers (NOLs) in spin-valve films for specular enhancement of giant magnetoresistance (GMR) effect. GMR values over 12% have been routinely obtained in spin-valve films with NOL, corresponding to a 30% specular enhancement over those without NOL. The consistency and robustness of the oxidation processes has been demonstrated by a very large GMR value ∼19% in a dual spin-valve film with the NOLs formed in both pinned layers, the oscillatory dependence of the interlayer coupling field on Cu layer thickness in specular enhanced spin-valve films and the uniform and repeatable film performance over 5 in. substrates.

An epitaxial wurtzite (WZ) Mg0.23Zn0.77O barrier based magnetic tunnel junction (MTJ), with electrode-barrier structure of Co0.30Pt0.70 (111)/Mg0.23Zn0.77O (0001)/Co (0001), was fabricated. The good crystallinity and tunneling properties were experimentally confirmed. Electrical and magnetic investigations demonstrated its high resistance-area product of 1.05 MΩ μm2, a maximum tunneling magneto-resistance (TMR) of 35.5%, and the existence of localized states within the tunneling barrier producing TMR rapid decrease and oscillation when increasing the applied bias voltage. The TMR value almost vanished at 200 K, which was attributed to the induced moment and strong spin-orbit coupling in Pt atoms at the Co0.30Pt0.70/Mg0.23Zn0.77O interface. Owing to the ferroelectric behavior in WZ-MgZnO materials, the fabrication of WZ-MgZnO barrier based MTJs deposited on a metallic ferromagnetic electrode will open routes for electrically controllable non-volatile devices that are compatible with CMOS technology.

We experimentally investigated the asymmetric transmission probabilities of spin-up and spin-down electrons at a (001)-Fe/Ag interface, which result in a highly spin-dependent interface resistance () that improves the magnetoresistive outputs of giant magnetoresistive devices whose ferromagnetic layers comprise only 3d transitional materials such as FeCo-based alloys. We quantitatively determined the spin-dependent interfacial parameters at FexCo100-x/Ag interfaces that were tuned by varying the Fe concentration x. Among the interfaces, the highest interface resistance of 0.65 mΩµm2 was obtained with an of 1.89 mΩµm2, which corresponds to ARF/N↑ ~ 1.08 mΩµm2 and ARF/N↓ ~ 7.98 mΩµm2 at a (001)-Fe/Ag interface.

Annealing time and temperature dependences of MR ratio in CoFe/Cu spin-valves were investigated. Thermal deterioration of MR ratio was well explained by considering two phenomena with effective activation energies of 2.16 eV and 1.57 eV for CoZrNb/NiFelCoFe/Cu/CoFe/FeMn spin-valves, and considering one phenomenon with a value of 2.49 eV for CoZrNb/NiFe/CoFe/Cu/CoFe/IrMn spin-valves, respectively. These values are in good agreement with activation energies of interdiffusion based on the vacancy mechanism. It is shown that no significant change in MR ratio is evaluated from the effective activation energies for the period of more than 10 years at 150/spl deg/C in CoZrNb/NiFe/CoFe/Cu/CoFe/IrMn spin-valve films.

We succeeded in developing CoFe spin valves with an antiferromagnetic Ir-Mn film. Ir-Mn single-layer films and spin valves of Ta(5 nm)/Ir-Mn(8 or 9 nm)/Co90Fe10(x nm)/Cu(3 nm)/Co90Fe10(3 nm)/NiFe(2 nm)/CoZrNb(10 nm)/ (x=2, 2.3, 2.6 nm), prepared by the sputtering method, showed the crystal structure of a fcc (111) preferred orientation. As-deposited CoFe spin valves with Ir-Mn exhibited an interfacial exchange coupling energy of J=0.192 erg/cm2 (Hua∼640 Oe at tCoFe=2 nm), that was the highest ever reported for as-deposited antiferromagnetic films, such as NiO, NiMn, and FeMn. Furthermore, CoFe spin valves with Ir-Mn exhibited a higher blocking temperature of 260 °C, and a higher MR ratio of 6.37% than the spin valves with FeMn film. After annealing, the MR ratio increased to 7.82%. On the other hand, the Hua decreased about 100 Oe after annealing. The Hua-T curve was, however, improved and the Hua at 100 °C increased to 400 Oe. The decrease in Hua was not observed after second annealing and seems to be st...

A perpendicular magnetic tunnel junction (pMTJ) device was fabricated using L10 ordered FePt electrodes, which were deposited on MgO(8 nm)/CrRu(10 nm)/TiN(4 nm) under-layers. It was found that the MgO/CrRu/TiN under-layer helps lower the required FePt deposition temperature to below 400 °C, and provides a well-ordered bottom L10 FePt electrode with root-mean-square (RMS) surface roughness close to 0.4 nm. Magnetoresistance (MR) ratio and resistance-area (RA) were measured at room temperature by the current-in-plane tunneling (CIPT) method from a lithographically unpatterned PMTJ sample and 138% and 6.4 kΩ μm2 were obtained, respectively. A PMTJ test pattern, with a junction size of 80 × 40 μm2, was also fabricated and showed a MR ratio and RA product of 108% and 4 ∼ 6 kΩ μm2, respectively, in good agreement with the CIPT measurements.

We report on the observation of anisotropic magnetoresistance (AMR) in vertical asymmetric nano-contacts (NCs) made through AlO$_x$ nano-oxide layer (NOL) formed by ion-assisted oxidation method in the film stack of Co/AlO$_x$-NOL/Pt. Analysis of NC formation was based on \emph{in situ} conductive atomic force microscopy and transmission electron microscopy. Depending on the purity of NCs from Al contamination, we observed up to 29% AMR ratio at room temperature.

Spin torque oscillations near zero magnetic fields were investigated in a nanocontact magnetoresistive device. A typical auto-oscillation mode was observed with high amplitude and narrow linewidth in a vortex domain state of the free layer around the zero field. The number of branches was reduced to a single one with an increase of current over the threshold value. As a result, we observed a linear frequency change between a wider field range across zero fields with a high amplitude and a narrow linewidth for the oscillation. The frequency response to small bipolar applied fields is applicable to a weak-field sensor.

The Ni nano constriction dots embedded in the Ta-nano-oxide layer (NOL) was prepared by the ion beam sputtering (IBS) method. After the various conditions of the oxidations, the structural analyses of the NOL were performed by RHEED, AES and in situ STM/AFM observations. From the current image of the conductive AFM for NOL, the periodically aligned metallic dots with the size around 5–10 nm were successfully observed. The mechanism of the formation of the self-organized aligned Ni nano constriction dots is discussed from the standpoint of the grain size, the crystal orientation, the preferred oxidation of Ta at the diffused interface.

A magnetic nanocontact spin valve (NCSV) was fabricated by inserting a TaO x nano-oxide layer (NOL) as the spacer layer. Current-perpendicular-to-film-plane (CPP) measurements revealed that the SV had a positive magnetoresistance (MR) ratio. When a high bias voltage was applied to the SV, the fine structure of the NOL changed i.e., the resistance and MR ratio of the device changed irreversibly. The change in device characteristics is attributed to a proportional change in the number of nonmagnetoresistive and magnetoresistive conductive channels in the SV upon high bias voltage application. The decrease in MR ratio accompanied the disappearance of the magnetic nanocontact, suggesting that the positive MR effect was partially due to the presence of magnetic nanocontacts.

We investigated the spin-transfer torque driven ferromagnetic resonance in nano-contact magnetoresistive (NCMR) devices with a current-perpendicular-to-plane spin-valve structure consisting of a FeCo layer, a FeCo-AlOx nano-oxide layer, a FeCo multilayer for the reference, a spacer, and free layers. In contrast with tunneling magnetoresistance devices with an AlOx spacer layer that shows a single resonant frequency, NCMR devices showed multi-resonant frequencies caused by free-layer resonance and other types of resonance appeared in a frequency region higher than that of the free-layer. We discuss these characteristic results in terms of the magnetic structure of the NCMR device, especially the free and reference layers around the nano-contacts.

Exchange bias from antiferromagnetic (AFM) oxides with a magnetoelectric (ME) effect has been studied for controlling ferromagnetic (FM) magnetizations by an applying electric field. However, thick ME oxides are needed for realizing the electrically controlled exchange biasing. Therefore, in this study the temperature dependencies of the training effect for the Cr2O3-nano-oxide-layer (NOL) are investigated for confirming the ME effect of the Cr2O3-NOL. The anomalous temperature tendencies of system dependent constant for exchange bias and magnetoresistance (MR), κHex and κMR, were observed, which are probably originated from the ME effect of the Cr2O3-NOL because (1) these anomalous temperature tendencies could not be obtained in the CoO-NOL spin valve and (2) the κHex and κMR are defined as the strength of the coupling between FM and AFM spins. It is remarkable result for us to confirm the possibility of the ME effect from the ultrathin Cr2O3 layer (less than 1 nm) because the ME effect was observed in o...

We have developed the FeCo nanocontact magnetoresistance (NCMR) with spin-valve structure [H. N. Fuke et al., IEEE Trans. Magn. 43, 2848 (2007)] which exhibits up to a MR ratio of 11%–12% at a resistance area (RA) of 0.3–0.55 Ω μm2. The nanocontact configurations were estimated at about 2 nm in in-plane diameter, 1.2 nm in thickness, and 0.55% in density for a RA∼0.5 Ω μm2 film based on in-plane current distribution by conductive atomic-force microscopy cross sectional transmission electron microscope images of the NCMR. The origin of the NCMR was discussed by comparing magnetic field dependence of resistance, with micromagnetics simulation based on the diffusive MR theory. It is found that our NCMR cannot be explained by diffusive domain wall theory or bulk scattering in free and pinned layers. It is likely that a theory on the basis of a ballistic MR consideration is needed to interpret our MR origin.

We have investigated the microwave oscillations due to a spin transfer effect induced by direct current in ferromagnetic nanocontact magnetoresistive (NCMR) elements with a current-perpendicular-to-plane spin-valve structure consisting of an FeCo/FeCo–AlOx nano-oxide layer/FeCo multilayer for the reference/spacer/free layers, respectively. Characteristic microwave oscillations were observed in the NCMR elements at different magnetization states induced by the application of a spin-polarized current, which are considered to be related to the introduction of a ferromagnetic NC to spacer layer (large interlayer coupling) and the resonance concerning the stability of the magnetization states of the free and reference layers around the NCs. A marvelously narrow full width at half maximum (FWHM) of l0–20 MHz is observed under a high applied magnetic field where the reference layer magnetization is slightly off axis relative to the pinned direction. By contrast, a wider FWHM of 80–600 MHz is observed at the magn...

For the structural characterization of a Co100−xFex nano-oxide layer (NOL), the exchange bias properties of the Co100−xFex-natural oxidized NOL in the specular spin-valve (SPSV) system were investigated. The exchange bias energy (Jex) increased monotonically with the increasing Fe content for the Co100−xFex-NOL. The enhancement of both the magnetoresistance ratio and the exchange bias field (Hex) was realized by increasing the Fe content in the Co100−xFex-NOL. It should be mentioned that Hex more than 800Oe is obtained by the insertion of Co30Fe70-NOL, even in NOL-SPSV, which is a remarkably higher pinning field than that ever reported on IrMn-SV. This high exchange bias field is considered to be realized by the formation of an Fe-rich fcc phase at the interface of IrMn.

We compared the specular spin-valve films with an Fe50Co50 nano-oxide layer (NOL) and a Co90Fe10 NOL in a pinned layer, prepared by natural oxidation (NO) and ion-assisted oxidation (IAO). For the IAO, an Ar-ion beam was used for the energy-assist effect during the oxidation, resulting in thermally stable NOL formation. With small oxygen exposures during the oxidation for the Fe50Co50 NOL by IAO, good ferromagnetic coupling through the NOL and high specularity at the NOL interface were concurrently obtained. Moreover, twisted coupling through the NOL was observed for the Fe50Co50 NOL by IAO for higher oxygen exposures. On the other hand, the NO did not cause large magnetoresistance (MR) enhancement for either the Co90Fe10 or Fe50Co50 NOLs, and the Co90Fe10 NOL by IAO caused weak magnetic coupling through the NOL, resulting in a small MR ratio. The Fe50Co50 NOL for small oxygen exposures is a good candidate for a final specular spin-valve film head for 100-Giga-bit per square inch recording.

Spin‐valve structures with a magnetic material buffer layer, CoNbZr/NiFe/Co90Fe10/Cu/Co90Fe10/Fe50Mn50, were prepared on a oxidized Si substrate. From x‐ray diffraction analysis, it was shown that the CoNbZr/NiFe buffer layer enhances the fcc (111) orientation of the spin‐valve structure on oxidized Si. After annealing, the giant magnetoresistance (GMR) ratio of Δρ/ρ=8% and the soft magnetic properties of Hc=0.1 Oe and Hk=2.8 Oe were obtained. The sensitivity of GMR, Δ(Δρ/ρ)/ΔH, of 1.4%/Oe is achieved.

The operating characteristics of a new type of torque sensor are described. The sensor consists of amorphous ribbons endowed with uniaxial anisotropy bonded to the shaft and corresponding pick-up heads. The heads are excited at 50kHz. The output signals from the sensors are processed to produce burst signals from which the torque is obtained. This sensor is easily mounted on a shaft, has a high detection sensitivity and operates under a low exciting current. It can be used to detect the torque at a given angular displacement, or for simultaneous detection of torque and revolution rate.

A torque sensor with a broad dynamic range employing amorphous ribbons in contact with a sensor head is described. A uniaxial anisotropy was induced in the FeCoSiB amorphous ribbons by magnetic field annealing. Ribbons with various K uo /? s used. As expected, a larger K uo /? s resulted in a broader dynamic range, but with lowered sensitivity. In stationary torque detection experiments, a sensitivity about 10 times that possible using strain gauges was achieved at a dynamic range of 2000 ?ST.