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We investigated current-perpendicular-to-plane (CPP) magnetotransport parameters of FexCo100-x/ Ag interfaces: interface specific resistance (ARF/N), extended interface resistance (AR* F/N), and spin scattering asymmetry (γ). We also investigated the dependence of interfacial parameters on the giant magnetoresistance effect with CPP geometry. For measuring these parameters, we prepared magnetic multilayers and pseudo spin valves (PSVs), combining the ferromagnetic (F) alloys Fe, Co, Fe50Co50, and Fe30Co70 with the nonmagnetic (N) metal Ag. In all cases, the largest ARF/N value was found to be ~0.68 mΩμm² with an enhanced AR* F/N value of ~1.9 mΩμm² for a (001)-oriented Fe/Ag interface, which suggests that spin-up and spin-down electrons on the Fermi surface have very different transmission probabilities. Such an interface can act as a spin filter through which only one type of electrons can pass. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The current-perpendicular-to-plane (CPP) giant-magnetoresistance (GMR) of spin valves with Fe50Co50 alloy was investigated. It has been reported that the Cu inserted in Fe50Co50 is effective for enhancing CPP-GMR. In this paper, we investigated the number of Cu lamination effect on CPP-GMR and clarified that higher CPP-GMR is obtained by decreasing the number of Cu layers. In order to ascertain the reason for this tendency, the crystalline structure and magnetization were examined. As a result, it was found that the d spacing of Fe50Co50 increases when the number of Cu layers is increased, although saturation magnetization does not change. [ABSTRACT FROM AUTHOR]

In this work, we present a suitable material for metal-based spin-valve in current-perpendicular-to-plane (CPP) geometry. The AΔR (A is the element size and ΔR is the change in resistance) was investigated for three kinds of free and pinned layers material, that is, Co[sub 90]Fe[sub 10], Fe[sub 50]Co[sub 50], and Fe[sub 50]Co[sub 50] with half-atomic Cu layers. When the free and pinned layers are 5 nm, AΔR is 1.0 mΩ/µm², 1.6 mΩ µm², and 2.9 mΩ µm², respectively. Moreover, the dual-type spin valve having Fe[sub 50]Co[sub 50] with half-atomic Cu layers achieved 5.2 mΩ µm². According to the free and pinned layers thickness dependence of AΔR, the spin-dependent resistance at the interfaces between ferromagnetic layers and spacer Cu is enhanced mainly by changing from Co[sub 90]Fe[sub 10] to Fe[sub 50]Co[sub 50], and the spin-dependent bulk resistance in free and pinned layers is enlarged by inserting half-atomic Cu layers. [ABSTRACT FROM AUTHOR]

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 B[sub s] 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%, ΔR[sub s] 1.5-2.0 Ω, H[sub c][sup ea]∼3 Oe, and λ[sub s]≤±0.5 ppm was obtained with a single CoFe free layer and synthetic antiferromagnetic pinned structure. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

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 magnetization state where the magnetization of the free layer just aligned to the antiparallel configuration against the magnetization of the reference layer. These characteristic results are discussed in terms of a spin dynamics mechanism induced by spin transfer torque in the free and reference layers around NCs. [ABSTRACT FROM AUTHOR]

We have reported that body-centered-cubic (bcc) Fe[SUB50]Co[SUB50] with ultrathin Cu layers has large spin-dependent bulk scattering and enhances AΔR of spin valves. In order to clarify the role of Cu, two series of samples with (Fe[SUB50]Co[SUB50] (1 nm/Cu) × 5 were prepared by two different sputtering machines. Machine A has a high rate, and machine B has a comparatively low rate. Both of AΔR in series A and B are increased by inserting thin Cu of about 0.1 nm, but they have a significant difference in Cu thickness dependence. While series A keeps high AΔR through the Cu thickness, AΔR in series B decreases when Cu is thickened. In order to find the reason for the difference, we took the extended x-ray absorption structure (EXAFS) spectra. By comparing AΔR and EXAFS, it was found that the very thin Cu of about 0.1 nm in Fe[SUB50]Co[SUB50] takes a body-centered-cubic bcc structure, namely a solid solution state. Cu of 1 nm in spin valves with high AΔR takes a bcc and face-centered-cubic (fcc) evenly, and that with a low AΔR is a fcc structure. These results indicate that the existence of the solid solution Cu in Fe[SUB50]Co[SUB50] is attributable to the enhancement of AΔR and are consistent with the report that Cu impurity in Fe and Co enhances the difference between the subband resistivity of up and down spins. [ABSTRACT FROM AUTHOR]

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. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

To understand the mechanism of current-confined-path formation for the current-perpendicular-to-plane type of giant magnetoresistive devices, we have investigated the evolution of an Al monolayer on the Cu (111) surface both by in situ scanning tunneling microscopy and by molecular dynamics simulation. Ultrathin Al nano-clusters were formed on the plateaus and step (or plateau) edges of the Cu surface in the as-deposited state. Upon annealing at 300 °C, Al atoms migrated toward the step edges by surface diffusion. As a consequence, nanometer-sized Cu channels not covered by Al clusters can be formed. These channels could serve as current-confined paths if subsequent mild Al oxidation is provided. [ABSTRACT FROM AUTHOR]

Presents a study on annealing time and temperature dependences of magnetoresistive (MR) ratio in CoFe/Cu spin-valves. Experimental procedures; Results; Conclusion.

A novel method is proposed for increasing the giant magnetoresistance (GMR) of dual spin valves of the CoFe/Cu/CoFe/Cu/CoFe type by inserting nano-oxide layers (NOLs) into the pinned layers. Using this method, MR ratio of 23.5% was obtained, a value equal to those of specular spin valves with antiferromagnetic oxide, e.g., NiO. This method allows the selection of metallic materials for the antiferromagnetic layer. In addition, we obtained the specularity factor of upper NOLs, 0.8, and that of lower NOLs, 0.7, by calculating Boltzmann equations taking into account the roughness of each interlayer. This model shows that the MR ratio would be 27.5% for dual spin valves with ideal NOLs. [Copyright &y& Elsevier]

Abstract: 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 5–10nm 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. [Copyright &y& Elsevier]