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Oblique Hanle effect (OHE) with magnetic field applied at an oblique angle ϑ (0 ≤ h ≤ 180°) was systematically investigated using the 3-terminal (3T) geometry with CoFe/SiO2/Si tunnel contacts. Clear Hanle-like signals with asymmetric voltage dependence are obtained for all angles. It is found that the asymptotic value of the OHE uniquely depends on the angle ϑ and its angular variation can be fitted well with both functions of cos²ϑ and 1/1-αΓ² cos²ϑ as predicted from spin injection and impurity-assisted magnetoresistance models, respectively. In addition, no Hanle signal is observed in tunnel junctions with spin-unpolarized CoFe/Ta/SiO2/Si structure, which is also understandable by both models. The experimental data in this study demonstrate clearly that further study should be still done to uncover the underlying physics of the Hanle-like signal in 3T tunnel contacts. [ABSTRACT FROM AUTHOR]

A positive magnetostrictive single layer (CoFe) and top-pinned spin-valve structure with positive magnetostrictive free (NiFe) and pinned (CoFe) layers were deposited on flexible polyethylene terephthalate film to investigate the changes in the magnetic properties in flexible environments, especially with a repetitive bending process. It was found that the stress, applied by repetitive bending, changes significantly the magnetic anisotropy of both layers in a single and spin-valve structure depending on the direction of applied stress. The changes in magnetic anisotropy were understood in terms of the inverse magnetostriction effect (the Villari effect) and the elastic recovery force from the flexibility of the polymer substrate. Repetitive bending with tensile stress transverse (or parallel) to the magnetic easy axis was found to enhance (or reduce) the magnetic anisotropy and, consequently, the magnetoresistance ratio of a spin-valve. The observed effects of bending stress in this study should be considered for the practical applications of electro-magnetic devices, especially magneto-striction sensor. [ABSTRACT FROM AUTHOR]

Based upon a bulk scattering model, we investigated the variation of giant magnetoresistance (GMR) behavior after thermal annealing at Ta=250 °C as a function of the top free layer thickness of a GMR spin valve with nano-oxide layers (NOLs). It was found that the enhancement of GMR ratio after thermal annealing is explained qualitatively in terms of the increase of active GMR region in the free layer and, simultaneously, the increase of intrinsic spin-scattering ratio. These effects are likely due to the improved specular reflection at the well-formed interface of NOL. Furthermore, we developed a modified phenomenological model for sheet conductance change (ΔG) in terms of the top free layer thickness. This modified model was found to be useful in the quantitative analysis of the variation of the active GMR region and the intrinsic spin-scattering properties. The two physical parameters were found to change consistently with the effects of thermal annealing on NOL. [ABSTRACT FROM AUTHOR]

Oxidation of an AlOx insulating barrier in a magnetic tunneling junction (MTJ) was carried out by a tilted-plasma oxidation method. It was found that the tilted-plasma oxidation induced a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and specific junction resistance (RA) of the MTJ. We found a linear relation in the TMR versus RA curve with positive and negative slopes for less- and overoxidized junctions, respectively, and a parabolic relation for optimally oxidized junctions. The crossover in the TMR versus RA curves provides an effective and useful way to optimize (and monitor) the oxidation condition of a tunneling barrier in MTJs especially of a tunneling barrier less than 10 Å thick. The tunneling junctions were also investigated after thermal annealing at various temperatures. The observations after thermal annealing were found to be consistent with transmission electrons microscopy images and a scenario of the partial formation of an additional ultrathin tunneling barrier at the top surface of the bottom magnetic layer. [ABSTRACT FROM AUTHOR]

We report an anomalous magnetotransport in a magnetic tunnel junction (MTJ) containing an Au dusting layer with Au thickness 0.6 nm at the Co/Al[sub 2]O[sub 3] interface, where the Co layer is pinned by the underlying FeMn layer. Despite its structure being exchange biased, the junction with the 0.6 nm Au layer exhibits symmetric magnetoresistance (MR) for both the applied magnetic field (H) directions, which is a typical MR feature without a pinning effect, and a low resistance state near H≈0 Oe. It is also found that the same MR features, i.e., symmetric MR and a low resistance state near H≈0 Oe, can be achieved in the MTJ without an Au insertion layer when the pinned Co moments are at an angle to the applied H direction. Based on measurements of the angular dependence of MR, we surmise that the anomalous MR is due to the effect of spin disorder in the Co layer, induced by the deposited Au layer. It is not likely that the anomalous effect is due to the quantum well state in the Au layer. [ABSTRACT FROM AUTHOR]

The voltage dependence of magnetoresistance (MR) and the low-frequency voltage fluctuation were studied in magnetic tunnel junctions with an AlN or an Al[sub 2]O[sub 3] barrier formed by plasma nitridation or oxidation. The junctions consist of free and pinned NiFe layers by a FeMn antiferromagnetic layer. For the Al[sub 2]O[sub 3] junction, the variation of half-reduction voltage of MR is about 50 mV from 401.3 mV in maximum to 351.4 mV in minimum depending upon the oxidation time. For the AlN junction, the less nitrided junction with a nitridation time of 120 s shows the higher-half-reduction voltage by about 100 mV than for optimally nitrided or oxidized ones. From the low-frequency voltage noise data, the less nitrided AlN junction shows larger 1/f noise magnitude compared with other junctions with an optimal condition, implying more defect states in the barrier due to unnitrided Al metals. In order to investigate the influence of nitrogen on ferromagnetic layer, another junction with an Al[sub 2]O[sub 3] barrier was made after the pinned NiFe layer was exposed to N[sub 2] plasma for 10 s. This junction reveals a lower MR and worse bias voltage dependence than any junctions studied here. The voltage dependence of MR, therefore, is likely influenced by the interface state rather than the defects in the barrier, although the two factors play an important role in determining MR. [ABSTRACT FROM AUTHOR]

Multiple Co/Pt bilayers were deposited on vertically aligned carbon nanotubes on an anodic aluminum oxide template. The structural and the magnetic properties of the nanoring arrays were investigated by varying the number of Co/Pt bilayers in the ranges 3-10 in multilayers with a Ta(3.0 nm)/[Co(1.0 nm)/Pt(1.5 nm)]n/Ta(1.0 nm) structure. The thickness and diameter of the nanorings increased with increasing repeat number. Compared with Co/Pt films, the Co/Pt nanoring arrays showed a larger coercivity. However, the magnetostatic interactions between the nanorings became dominant in the reversal behavior and caused a nonsquare hysteresis loop. Giant magnetoresistance structures consisting of multiple Co/Pt bilayers and a thick Cu spacer exhibited magnetization curve that were in good agreement the summation of the moments of layers with varied bilayer repetition. [ABSTRACT FROM AUTHOR]

We investigated the top and bottom interfaces of a CoFeB/MgO/CoFeB tunnel junction using transmission electron microscope (TEM) and x-ray photoemission spectroscopy (XPS) in order to understand the origin of the asymmetry of dI/dV in terms of bias polarity. It was found, from a TEM image, that there is no clear cut at the top interface, while the bottom interface has relatively clean boundary. Furthermore, XPS data show that more hydroxides were formed at the top interface than at the bottom interface. These indicate that the hydroxides would hinder the epitaxial crystallinity at the interface in CoFeB/MgO/CoFeB tunnel junctions. Therefore, it is most likely that the asymmetry of dI/dV is caused by the disappearance of minority Bloch state, which is closely correlated with the existence of hydroxides at the top interface of a CoFeB/MgO/CoFeB tunnel junction. [ABSTRACT FROM AUTHOR]

We used streptavidin-coated magnetic particles (Dynabeads® M-280) for an immunochromatographic test, instead of colloidal gold particles, which was widely used in a conventional technique. The concentration of magnetic particles in a membrane was quantitatively analyzed by using a giant magnetoresistance (GMR) sensor with a sensitivity of 0.17%/Oe. As a specific zone with a localized concentration of the magnetic particles passed through a GMR sensor, it was observed that the magnitude of sensing signals is proportional to the density of magnetic particles. Therefore, this result suggests that a GMR sensor, which was studied in this paper, can be used for the quantitative detection with a high sensitivity of specific analytes in the immunochromatographic assays, when the analytes were coated on magnetic particles. [ABSTRACT FROM AUTHOR]

On a single crystal of YMn4Al8, we investigated specific heat and temperature-dependent magnetization M(T) and resistivity ρ(T) with field and current, respectively, parallel and perpendicular to the c axis. A few features are observed on single crystals and not on polycrystalline samples. While we found no noticeable anisotropy in M(T), there is a significant anisotropy in ρ(T), i.e., ρ∥(T)>ρ⊥(T) for T>43 K and ρ∥(T)<ρ⊥(T) for T<43 K, where ρ∥(T) and ρ⊥(T) are ρ(T)’s with current parallel and perpendicular to the c axis, respectively. In addition, a significant increase of γ, an electronic specific heat contribution, is found at low temperatures, resulting in γ(T=2 K)=130 mJ/mol K2. [ABSTRACT FROM AUTHOR]

Breakdown characteristics of the magnetic tunnel junctions (MTJ) with different junction areas of S = 200 μm[SUP2] and S = 0.5 μm[SUP2] are investigated under constant voltage stress. The breakdown process is found to be quite different for the two junction areas. For the large junctions with S = 200 μm[SUP2], magnetoresistance (MR) ratio decreases gradually with increasing time of constant voltage stress and lasts for 10-30 min. The low frequency 1/f noise power also increases with increasing stress time due to the Johnson and shot noises, caused by current flowing through ohmic shorts or pinholes across tunnel barrier. Meanwhile, the junctions with S = 0.5 μm[SUP2] show abrupt junction breakdown after stress time of 1-7 h. There is no significant change in both MR ratio and its bias dependence during the voltage stress. In particular, soft-breakdown events are observed before total breakdown occurs. The junction breakdown of small junction area is of intrinsic nature of the junction while the one of large junction area is due to extrinsic factors. [ABSTRACT FROM AUTHOR]

We investigated the effects of nitrogen plasma treatment on top surface of Fe pinned layer for short times (t[SUBex] =0, 10, 30, and 60 s) in magnetic tunnel junctions and annealing of the junctions. The nitrogen-treated junctions show much reduced magnetoresistance (MR) ratio and significantly lower resistance-area (RA) products compared with the untreated junction, i.e., MR &ap; 3%, RA &ap; 30 kΩ μm[SUP2] for t[SUBex] =10 s and MR &ap; 10%, RA &ap; 60 kΩ μm[SUP2] for t[SUBex] =0 s. The untreated junction showed enhanced MR ratio up to about 17% and higher RA (&ap;70 kΩ μm[SUP2]) upon thermal annealing at T[SUBa] =230 °C, as expected. For the nitrogen-treated junctions, while the MR ratio also increases up to about 16% upon annealing at T[SUBa] =230 °C, which is almost the same value as the one of the optimal reference junction, the RA values of the annealed junctions still keep as low as their initial values. We believe that the redistribution of nitrogen during the annealing process is responsible for the change of properties of nitrogen-treated junction. The bias dependence of MR and the estimation of effective barrier height and thickness are studied and found to be consistent with the observed changes in nitrogen-treated junctions. [ABSTRACT FROM AUTHOR]

We performed three-terminal (3T) Hanle measurement for two types of sample series, CoFe/SiO2/n+-Si and Cu/SiO2/n+-Si, with various tunnel resistances. Clear Hanle signal and anomalous scaling between spin resistance-area product and tunnel resistance-area product were observed in CoFe/SiO2/n+-Si devices. In order to explore the origin of the Hanle signal and the impurity-assisted tunneling effect on the Hanle signal in our devices, Hanle measurement in Cu/SiO2/n+-Si devices was performed as well. However, no detectable Hanle signal was observed in Cu/SiO2/n+-Si, even though a lot of samples with various tunnel resistances were studied in wide temperature and bias voltage ranges. Through a comparative study, it is found that the impurity-assisted tunneling magnetoresistance mechanism would not play a dominant role in the 3T Hanle signal in CoFe/SiO2/n+-Si tunnel junctions, where the SiO2 was formed by plasma oxidation to minimize impurities. [ABSTRACT FROM AUTHOR]

We investigated the out-of-plane anisotropy of Co[sub50] Fe[sub50]/Tb multilayer film with changing the thickness of Tb layer and applying an inplane filed of 200 Oe during film deposition. A strong out-of-plane anisotropy was found only for the multilayer with small thickness of Tb layer (t[subTb] = 1 nm) and was suppressed significantly by the application of an inplane magnetic field of 200 Oe during deposition, resulting in an inplane anisotropy. It was also found that the application of the magnetic field caused the enhanced intermixing between CoFe and Tb layers to form Co-Tb and Fe-Tb alloys at the interface of the layers. While the origin of the out-of-plane anisotropy and the change of the out-of-plane to inplane anisotropy with the application of inplane field of 200 Oe are not understood completely, it seems that there is a strong correlation between the out-of-plane anisotropy and the formation of the alloys and the stress at the interface. [ABSTRACT FROM AUTHOR]

A correction to the article "Effects of repetitive bending on the magnetoresistance of a flexible spin-valve" that was published in the previous issue is presented.

Experimental results are demonstrated for the cracking of nominally compressed AlyGa1-yN layers grown on AlxGa1-xN buffer layers with smaller lattice constants (y≤x). The authors present a theoretical analysis showing that the inclination of pure edge threading dislocation lines effectively reduces the compressive stress, causing relaxation, and after reaching a certain thickness begins to generate the tensile stress gradient responsible for cracking. The critical layer thickness for crack nucleation in such a gradient elastic field has been found. The results of the modeling are in good agreement with experimental observations of crack onset in nominally compressed nitride layers [ABSTRACT FROM AUTHOR]

We introduce a CoFe/Tb multilayer film as a sensing layer of alternating giant magnetoresistance (GMR) spin-valve sensors for use in a high-field measurements. The CoFe/Tb sensing layer has lower in-plane anisotropy than a single CoFe sensing layer and allows the alternating GMR sensor to show a high sensitivity, ∼0.4 MR[%]/kOe, when the sensing layer structure is [CoFe(1.92 nm)/Tb(1.22 nm)] × 2. This sensitivity is about four times larger than previously reported values. In addition, it was found that the working range of the sensor could be easily tuned by varying the CoFe thickness in the reference layer. Therefore, this study is encouraging not only for GMR alternating spin-valve sensor applications, but also for the development of tunneling magnetoresistance based alternating sensor applications with considerably higher sensitivities. [ABSTRACT FROM AUTHOR]

Giant magnetoresistance (GMR) signals and the magneto-optic Kerr effect (MOKE) are combined to investigate the asymmetric domain wall (DW) motion in a GMR spin-valve stripe consisting of a wire and a circular ring. In the propagation of a tail-to-tail DW, the left-hand side, top-half ring, bottom-half ring, and the right-hand side are reversed in sequence. However, in the propagation of a head-to-head DW, the left-hand side, bottom half-ring, right-hand side, and top-half ring are switched in sequence. In addition, the critical current density for DW depinning shows asymmetric behavior. For tail-to-tail DW depinning, the critical current density of negative current pulses are lower than that of current pulses in the positive direction, and vice versa for head-to-head DW depinning. [ABSTRACT FROM AUTHOR]

We investigated a magnetic tunnel junction (MTJ) with a tunnel barrier formed by N[sub 2]O plasma. Compared with a MTJ with a tunnel barrier formed by conventional O[sub 2] plasma, the MTJ fabricated with N[sub 2]O plasma shows much lower specific junction resistance and a comparably high tunneling magnetoresistance ratio. In particular, it was found that N[sub 2]O plasma oxidation is quite important in the junction with a thin tunnel barrier, for which O[sub 2] plasma cannot be used. From x-ray photoelectron spectroscopy, we observed that N[sub 2]O plasma oxidation leads to the slight nitridation of the Al[sub 2]O[sub 3] layer and significantly reduces the oxidation of the bottom electrode, especially for a thin tunnel barrier. Thus, we conclude that the use of N[sub 2]O plasma in forming the tunnel barrier is effective for achieving a low junction resistance and for minimizing the oxidation of the bottom electrode during plasma oxidation in MTJs. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this study, Hall effects, magnetoresistance, and low temperature resistivity of single crystalline SrPd2Ge2 were measured. The sign change of the Hall coefficient from negative to positive with increasing temperature in the normal state and the violation of Kohler's rule in magnetoresistance data were observed. These results suggest that electrons and holes would contribute together to the formation of multi bands and that the scattering on the Fermi surface is anisotropic, which should be taken into account for the transport properties of SrPd2Ge2. In addition, we estimated the upper critical field at T = 0 K, Hc2(0) = 6.1 kOe, from the temperature-dependent electrical resistivity measurement down to 0.35 K. Including this, we discuss the nature of SrPd2Ge2 single crystals. [ABSTRACT FROM AUTHOR]

On a single crystal of YMn4Al8, we investigated specific heat and temperature-dependent magnetization M(T) and resistivity ρ(T) with field and current, respectively, parallel and perpendicular to the c axis. A few features are observed on single crystals and not on polycrystalline samples. While we found no noticeable anisotropy in M(T), there is a significant anisotropy in ρ(T), i.e., ρ∥(T)>ρ⊥(T) for T>43 K and ρ∥(T)<ρ⊥(T) for T<43 K, where ρ∥(T) and ρ⊥(T) are ρ(T)’s with current parallel and perpendicular to the c axis, respectively. In addition, a significant increase of γ, an electronic specific heat contribution, is found at low temperatures, resulting in γ(T=2 K)=130 mJ/mol K2. [ABSTRACT FROM AUTHOR]