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Read heads using current-perpendicular-to-plane (CPP) giant magnetoresistance sensors have been fabricated and tested under highdensity recording conditions. A magnetoresistance of 5.5% and shield-to-shield spacing of 45 nm have been achieved by using an all-metal single-spin-valve with Heusler-alloy-based free and reference magnetic layers. Read heads with magnetic read widths ~45 nm were tested on perpendicular media, resulting in signals above 1 mV and signal-to-noise ratio ~30 dB. Linear densities in excess of 1050 kbpi were achieved with thermal fly-height control, compatible with recording areal densities of ~ 400 Gb/in (2). Current-induced spin-torque effects in the recording head were observed to result in rapid performance degradation above a threshold bias voltage of about 75 mV, corresponding to current densities > 10 (8) A/cm (2). Index Terms--CPP-GMR, magnetic recording, read-head, spin-valve.

The magnetics and magnetotransport of current perpendicular to the plane (CPP) giant magnetoresistive (GMR) spin valves utilizing thin CoPt hard magnet pinning layers on Cr seed layers are investigated. Free layer softness does not suffer from the proximity to the CoPt hard magnet due to the relatively thick spacer layers compatible with CPP GMR sensors.

Research into thermally assisted decay of pinning in polycrystalline exchanged biased systems is presented. It is concluded that thermally activated reversal of the pinned layer is a factor in the design of spin valves. The decay rates at operating temperatures are sufficiently large to totally destabilize the pinned layer over the lifetime of a sensor.

Interlayer exchange interactions and exchange anisotropy in polycrystalline antiferromagnetic CoO-NiO thin film superlattices were investigated. The results showed that the effects of magnetic coupling reach through oxide layers less than 55 angstroms thick. CoO layers less than 20 angstroms in thickness were strongly coupled to the NiO layer and the CoO-layer ordering temperature approximated the NiO value.

Giant magnetoresistance (GMR) in heterogenous Cu-Co and Ag-Co alloy thin films was investigated. The results showed that GMR in the Ag-Co sample was greater than that in the Ag-Co film. This was attributed to the smaller amount of dissolved Co in the Ag matrix. In addition, GMR was inversely proportional to the precipitate particle size. This indicated that Co-rich clusters with sizes greater than or equal to 20 angstroms were most effective for spin dependent scattering.

In multilayer systems with exchange-coupled layers such as exchange-spring magnets, interfacial pinning can give rise to spiral domain walls and other complex magnetic structures that are sensitive to temperature, relative layer thicknesses, etc. Though these spin structures develop in subsurface layers, the depth-dependent magnetic profile can be fully characterized using polarized neutron reflectivity (PNR). In order to obtain the profile of the vector magnetization as well as the chemical composition, these data are typically analyzed using software in which the sample is described by a series of flat layers. This approach is cumbersome for continuously varying depth profiles, such as magnetic spirals, since the magnetic layers must be artificially subdivided to mimic the smooth changes in the vector magnetization. Thus, we have developed a flexible PNR fitting program in which users can specify a formula for the model (e.g., flat, power law, or piecewise polynomials). The program can easily be extended to handle simultaneous fitting of multiple data sets from measurements made with different techniques (such as PNR and X-rays) with constraints between the models. Index Terms--Depth-dependent magnetization, exchange springs, polarized neutron reflectometry, spiral domain wall.

Improvements in exchange-biased spin valves have come from control of the grain size and the addition of a ruthenium layer. In this work the GMR ratio, the exchange field and blocking temperature for three sets of spin valves with varying IrMn thickness were measured. Two sets of samples with grain sizes of 10 nm, and one with a grain size of 30 nm were studied. One of the 10 nm grain size sets has a Ru layer separating the antiferromagnet from the Ta capping layer. The GMR ratio at 5 K depends on the grain size, but shows no dependence on the presence of the Ru layer, with larger grain samples having a higher GMR ratio. The exchange fields at 5 K are independent of grain size. However, the samples with the Ru layer show a higher exchange field at 5 K than those without. The blocking temperature for the small grain sets with and without Ru correlate very well with the exchange field. Ta in contact with the IrMn causes a magnetically 'dead' region. Index Terms--Exchange bias, giant magnetoresistance, grain-size effects, spin valves.

We have investigated the mechanism of weak exchange bias for a spin valve with threshold layer antiferromagnetic (AFM) thickness using giant magnetoresistance (GMR) and polarized neutron reflectometry (PNR). Results show that the sample exhibits instantaneous switching of the free layer followed by a gradual reorientation of the magnetization in the pinned ferromagnetic layer via domain wall formation. During subsequent field cycles, we found that relaxation in the pinned ferromagnetic (FM) layer is induced not only by an increasing field, but also in a static field over a relatively long time scale. Index Terms--Antiferromagnetic (AFM) materials, giant magnetoresistance (GMR), interface magnetism.

Magnetic recording read heads have been fabricated and tested using a dual-spin-valve (dual-SV) current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) sensor stack. Thin IrMn antiferromagnetic layers are used for top- and bottom-pinned layers, resulting in a total sensor stack height of 50 nm. Operational read heads with physical sensor trackwidths ranging from 60 to 30 nm have been achieved. Successful readback testing is obtained using perpendicular recording media, with observed magnetic read widths as low as 46 nm. Index Terms--Current-perpendicular-to-plane (CPP) giant magnetoresistive (GMR) read heads, dual spin-valve, magnetic recording.

Dual IrMn-pinnned current-perpendicular-to-plane giant magnetoresistive sensors for magnetic recording heads were investigated and their noise characteristics were compared to similar standard single sensors, using test structures with sizes down to 50 nm. The results of the comparison revealed that the intrinsic signal DELTA RA in the dual spin valves (SVs) increased by a factor of about 2 compared to the single SV, while the extra parasitic resistance of the second IrMn-pinned layer limited the DELTA R/R increase to a factor of about 1.5.

The magnetoresistance of antiparallel (AP) coupled self-pinned spin valves was measured utilizing Ir as a coupling layer. The magnetoresistance ratio increased quasilinearly from 2.2% to 4.0% with a reference layer thickness as expected from the Valet-Fert model in the long spin diffusion length limit.

We have studied the effects on the exchange bias of decreasing the antiferromagnetic layer to the Angstrom-scale regime in order to shed light on the minimum required thickness of the antiferromagnet. We have deposited IrMn layers between 0.2 and 2 nm on spin valves and measured the exchange bias by examining hysteresis loops at 5 K using the giant magnetoresistance of the spin valves. The exchange bias persists for IrMn thicknesses down to 0.4 nm and has a maximum at 1.6 nm. Because the ultra-thin layers create an exchange field, the origin of at least one component of exchange biasing must have a similarly short length scale. Index Terms--Antiferromagnetic materials, giant magnetoresistance, interface magnetism.

Back/front polarized neutron reflectometry was used for examining the field-dependent layer switching in a CoFe2O4/CoFe10 bilayer. A magnetic twist in intermediate fields is observed in the interface or in the magnetically hard CoFe2O4 layer.

Thin silicon layers can be used to good effect in spin valve sensors. The results suggest that films grown on Si have larger grains than those with Ru seed layers.

The low temperature properties of IrMn spin valves Ti(50 A)/NiFe(40 A)/Co(8 A)/Cu(30 A)/Co(30 A)/IrMn(t A)/Ti(50 A) are examined. Giant magnetoresistance (GMR) is adversely affected at lower temperature with thin IrMn.

The magnetic structure of reactively-sputtered CoO/NiO thin films was investigated using neutron diffraction analysis. The results showed that collinear antiferromagnetic order propagated through several bilayers. The magnetic moment for 36 angstrom period superlattices developed at the same time in the NiO and CoO layers at a Neel temperature between the values for bulk CoO and NiO.

The effects of domain wall formation on the magnetoresistance (MR) are examined by studying the depth profile of the vector magnetization in comparable spin valves. The transition from perpendicular to parallel domain wall formation has occurred for pinned layer thicknesses greater than 4 nm and the magnitude of the maximum MR has depended on the type of domain wall.

The distribution of switching times in spin-transfer switching induced by fast current pulses is measured in spin valves and MgO-based magnetic tunnel junctions. The thermally activated, nonuniform switching has yielded a switching probability that has increased with the pulse duration.

The magnetotransport properties of current perpendicular to the plane giant magnetoresistive spin valves are examined by using [([[Co.sub.x][Fe.sub.100-x]).sub.100-y][Al.sub.y] . The spin-torque measurements have shown that the spin-torque current threshold is lower in CoFeAl spin valves than in standard CoFe spin valves.

The magnetization dynamics induced by spin transfer torque (STT) in CoFe/Ru/CoFe/Cu/NiFe nanopillars using Landau-Liftshitz-Gilbert micromagnetic simulations including the STT term given Slonczewski and a Gaussian thermal random force is studied. The simulations clearly show the probabilistic switching behavior.

An exchange biased bilayer system which induces a transient internal field pulse with a picosecond rise, triggering a precessional response of the ferromagnetic layer of the exchange-coupled bilayer is proposed as a specific material test system to study the spin damping phenomena in real time. It is seen that that the exchange bias can effectively modify the relaxation of photoexcited exchange-coupled spins.

An exchanged bias spin valve with an antiferromagnetic 1.6 nm IrMn layer is investigated using giant magnetoresistance and polarized neutron reflectometry to probe separately the free and pinned CoFe layers. The results confirm that the two ferromagnetic CoFe layers are aligned in parallel in saturating fields.

The spin dependent mean free path in Co90Fe10 is determined as a function of temperature down to 5 K using two different spin valve structures. The results revealed that at low temperatures, the spin mean free path of 9 nm exceeds the typical thickness of the ferromagnetic layers in spin valves.

The reversal in the aniferromagnetic layer in IrMn-based exchange-biased systems is examined. The hysteresis loop is derived exclusively from the degree of order in the antiferromagnet and the peak in the coercivity does not occur at the mean blocking temperature.

Exchange-biased multilayers with IrMn thicknesses from 2 to 80 Angstrom with 50-Angstrom Ti over- and underlayers are discussed. IrMn layers grown with a dominant hcp phase show an enhanced effect in the magnetization.