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Correlation between the amplitude of the spin accumulation signals and the effective barrier height estimated from the slope of the log (RA) - tMgO plot (RA: resistance area product, tMgO: thickness of MgO tunnel barrier) in CoFe/MgO/n+-Si junctions was investigated. The amplitude of spin accumulation signals increases with increasing effective barrier heights. This increase of the amplitude of spin accumulation is originated from the increase of the spin polarization (PSi) in Si. The estimated absolute values of PSi using three-terminal Hanle signals are consistent with those estimated by four-terminal nonlocal-magnetoresistance (MR) and two-terminal local-MR. To demonstrate large spin accumulation in Si bulk band and enhance the local-MR through Si channel, these results indicate that the increase of the effective barrier height at ferromagnet/(tunnel barrier)/ n+-Si junction electrode is important. [ABSTRACT FROM AUTHOR]

For development of a spin-filtering device with a ferromagnetic barrier, very thin Co-ferrite layers are prepared by the plasma oxidization of the Co[Fe.sub.2] surface deposited on MgO(001) single crystal substrates and postannealing process. Spin-filtering junctions consisting of Co[Fe.sub.2]/(MgO/)Co-ferrite/Ta are fabricated and exhibit nonlinear J-V curves. By the insertion of a MgO layer, clear independent rotation of two magnetic moments is observed. Index Terms--Co-ferrite, spintronics, spin-filtering devices, spin-polarized current sources.

The crystal structure and magnetic moment of the [Co.sub.2]FeAl and [Co.sub.2]FeSi films deposited onto thermally oxidized Si and MgO(100) single-crystal substrates are investigated, along with the structural effect on the tunnel magnetoresistance (TMR) of the magnetic tunnel junctions using [Co.sub.2]FeZ (Z=Al or Si). The substrate and post annealing temperatures, changed the structure, in which the fully epitaxial and polycrystalline [Co.sub.2]FeAl and [Co.sub.2]FeSi films were obtained with different disorder structure.

We study current-perpendicular-to-plane (CPP) geometrical giant magnetoresistance (GMR) and magnetic switching property for single spin-valves (SVs). Applying a synthetic antiferromagnet (SyAF) instead of a single ferromagnet film as a free layer, the resistance-change area product [DELTA]RA of the SVs is strongly enhanced from ~ 1.84 m[ohm] [micro][m.sup.2] to ~ 16.8 m[ohm]/[micro][m.sup.2] and the CPP-GMR ratio changes from 0.8% to 3.6%. The study of the magnetic switching behavior by both experiment and single-domain thermal activation modeling shows that the SVs with SyAF as a free layer approaches a single-domain magnet even with a low aspect ratio 1 as long as its size diminishes to ~ 0.18 [micro][m.sup.2]. Because of the single-domain structure, the SVs with SyAF give a size-independent magnetic switching field when the aspect ratio is 1. Index Terms--Giant magnetoresistance (GMR), magnetic domains, spin-valves (SVs).

The structural and magnetic properties of the Co2Cr(sub 1-x)Fe(sub x)Al films in a wide composition range are discussed. The maximum tunneling magnetoresistance at room temperature was obtained as 19 percent for x=0.4.

Annealing temperature dependence of the tunnel magnetoresistance (TMR) ratio for magnetic tunnel junctions with CoFe[O.sub.x] inserted in the pinned layer was investigated. A junction with a CoFe/CoFe[O.sub.x]/CoFe pinned layer exhibited TMR ratios of 46.5% and 42.5% after annealing at 350[degrees]C and 375[degrees]C, respectively. The reason for the improvement of the thermal stability is related to oxygen diffusion from the CoFe[O.sub.x] layer, and there is a possibility that CoFe[O.sub.x] plays the role of a Mn (in Mnlr exchange layer) diffusion barrier. Index Terms--Annealing, CoFe[O.sub.x] layer, thermal stability, tunneling magnetoresistance.

We study in detail how the bias voltage (Vbias) and interface resistance (RA) depend on the magnitude of spin accumulation signals (|ΔV| or |ΔV|/I, where I is current) as detected by three-terminal Hanle measurements in CoFe/MgO/Si on insulator (SOI) devices with various MgO layer thicknesses and SOI carrier densities. We find the apparent maximum magnitude of spin polarization as a function of Vbias and the correlation between the magnitude of spin accumulation signals and the shape of differential conductance (dI/dV) curves within the framework of the standard spin diffusion model. All of the experimental results can be explained by taking into account the density of states (DOS) in CoFe under the influence of the applied Vbias and the quality of MgO tunnel barrier. These results indicate that it is important to consider the DOS of the ferromagnetic materials under the influence of an applied Vbias and the quality of tunnel barrier when observing large spin accumulation signals in Si. [ABSTRACT FROM AUTHOR]

Interlayer exchange coupling in magnetron-sputtered FePt/Ru/Fe trilayers has been investigated. The thickness dependence of in-plane magnetic properties of FePt thin films was investigated and a 12.5-nm-thick FePt film showed both high coercivity and good squareness. The exchange coupling between FePt and Fe layers through a Ru interlayer was obtained with an oscillatory period of about 1 nm. A 0.5 nm Ru layer produced a ferromagnetic coupling between the two magnetic layers and the saturated magnetization is considerably improved through interlayer exchange coupling with Fe. [ABSTRACT FROM AUTHOR]

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The structural, magnetic, and transport properties are investigated for full-Heusler alloy Co2(Cr1-xFex)Al (CCFA) thin films sputtered on thermally oxidized Si substrates at room temperature (RT). X-ray diffraction reveals that the films possess the B2 structure for x=0, decrease the atomic site ordering by substituting Fe for Cr (0.4<=x<=0.6), and form the A2 structure for x=1. Both the magnetic moment and the Curie temperature of the films increase with increasing Fe content (x), although the moment for x<1 is significantly smaller than that of the calculated value for the L21 structure. Magnetic tunnel junctions (MTJs) with CCFA films as either upper or bottom ferromagnetic layers are also fabricated by using metal masks. The maximum tunneling magnetoresistance (TMR) at RT for the MTJ was observed to be 19.1% for x=0.4 with the CCFA film as an upper ferromagnetic layer, despite the atomic disorder of the CCFA film. This is consistent with our previous TMR observation with the CCFA film as a bottom ferromagnetic layer, indicating that the CCFA film even with the B2 structure is a good candidate for future spintronic devices due to its disorder tolerance, high reproducibility, and large spin polarization. [ABSTRACT FROM AUTHOR]

Magnetic tunnel junctions (MTJs) using a synthetic ferrimagnet (SyF) free layer consisting of Co[sub 90]Fe[sub 10]/Ru/Co[sub 90]Fe[sub 10] were deposited on a thermally oxidized Si substrate using an ultrahigh-vacuum sputtering system, and were patterned into micron to submicron sizes using electron-beam lithography and Ar ion milling. Magnetic switching properties and tunneling magnetoresistance (TMR) were investigated. A SyF free layer can maintain high remanence even for the aspect ratio of 1, and exhibits a size-independent switching field in all element widths from 0.25 to 16 μm investigated. Additionally, these MTJs show large TMR ratio up to 40% after annealing at 250 °C for 60 min. These results demonstrate that a SyF free layer can be applied to future spintronics nanodevices. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

[Co.sub.2]Fe[Al.sub.0.5][Si.sub.0.5] full Heusler alloy thin films are prepared by using a molecular beam epitaxy system on Cr buffered MgO single crystal substrates and their structural and magnetic properties are examined. The studies have shown that the tunnel magnetoresistance ratio of the junction with Al-oxide barrier has larger asymmetric bias voltage dependence when compared with that of MgO barrier and the negative tunnel magnetoresistance ratio at high negative bias voltage is seen for both junctions.

Magnetization reversal process and the critical diameter for single and multidomain of Co/Pt multilayer dot are examined by detecting anomalous Hall effect of a single dot. The critical diameter for single domain state has increased with the perpendicular anisotropy constant and has coincided well with the magnetic domain size of the continuous films.

The reversal behavior in a single nanomagnet of Co/Pt is studied by using anomalous Hall effect measurement technique. The results have shown that the reversal mechanism is dominated by the magnetic anisotropy and is invariable in the temperature range 100-300 K.

Both polycrystalline Co2CrAl and epitaxial Co2FeAl full Heusler alloy thin films with the perfectly ordered L2(sub 1) structure are grown onto GaAs(001) substrates at 673 K. The element specific magnetic moment per Co atom is found to agree well with the theoretical calculation, while that per Fe atom is decreased.

An optimized condition is used to successfully grow both L2(sub 1) polycrystalline Co(sub 2)CrAl and epitaxial L2(sub 1)-structured Co(sub 2)FeAl films onto GaAs(001) substrates. These films are used to fabricate the magnetic tunnel junctions (MTJs), which show 2% tunnel magnetoresistance (TMR) for the Co(sub 2)CrAl MTJ at 5K and 9% for the Co(sub 2)FeAl MTJ at room temperature (RT).

The structural, magnetic, and transport properties of full-Heusler alloy Co2(Cr(sub 1-x)Fe(sub x))Al (CCFA) thin films are investigated. The films are likely to posses not only the B2-type disorder but the atomic disorder between Co and Cr for x

Magnetic switching field and magnetic domain structures for micron to submicron size SyAF elements are discussed. It is believed that the SyAF is a valid structure for both achieving a single domain structure and reducing the switching field.

Local magnetoresistance (MR) through silicon (Si) and its bias voltage (Vbias) (bias current (Ibias)) dependence in ferromagnet (FM)/MgO/silicon-on-insulator lateral spin valves are investigated. From the experimental measurements, we find that the local-MR through Si increases with increasing Vbias. This anomalous increase of local-MR as a function of Vbias can be understood by considering the standard drift-diffusion theory improved by taking into account the difference in the interface resistances and first order quantum effect between FM/MgO/Si (source) and Si/MgO/FM (drain) interfaces. The interface resistance dependence on experimentally obtained local-MR ratios also agrees with the improved standard spin diffusion theory. These results indicate that experimentally observed local-MR is certainly related to the spin signal through the Si bulk band. [ABSTRACT FROM AUTHOR]

The authors fabricated Co2FeAl0.5Si0.5 full Heusler alloy thin films by using a molecular beam epitaxy system on Cr buffered MgO single crystal substrates and investigated their structural and magnetic properties. It was revealed that Co2FeAl0.5Si0.5 films formed ordered L21 and B2 structures after annealing above 500 °C and below 400 °C, respectively. Then magnetic tunnel junctions with these electrodes and Al-oxide or MgO barriers were also fabricated, and the bias voltage dependence of tunnel magnetoresistance ratio was investigated. It was found that the tunnel magnetoresistance ratio of the junction with Al-oxide barrier has a larger asymmetric bias voltage dependence compared with that with MgO barrier, and the negative tunnel magnetoresistance ratio at high negative bias voltage is observed for both junctions. [ABSTRACT FROM AUTHOR]

We have investigated the crystal structure and magnetic moment of the Co2FeAl and Co2FeSi films deposited onto thermally oxidized Si and MgO(100) single-crystal substrates, and the structural effect on the tunnel magnetoresistance (TMR) of the magnetic tunnel junctions (MTJs) using a Co2FeZ (Z=Al or Si). The structure was changed by the substrate and postannealing temperatures, in which the fully epitaxial and polycrystalline Co2FeAl and Co2FeSi films were obtained with the different disorder structure. The magnetic moment of Co2FeAl films was found to be uninfluenced by the crystal structure. Spin-valve-type MTJs consisting of Co2FeZ(100 nm)/Al(1.2 nm)-oxide/Co75Fe25(2 nm)/IrMn(10 nm)/Ta(60 nm) were fabricated (Z=Al or Si) on thermally oxidized Si and MgO(100) single-crystal substrates. The maximum TMR obtained is about 50% at room temperature for MTJs with Co2FeAl films, regardless of the crystal structure of Co2FeAl. [ABSTRACT FROM AUTHOR]

Both polycrystalline Co2CrAl and epitaxial Co2FeAl full Heusler alloy thin films with the perfectly ordered L21 structure have been grown onto GaAs(001) substrates at 673 K. The Co2FeAl films, in particular, consist of an almost single phase with the crystalline relationship of Co2FeAl(001)(110) ‖GaAs(001)(110). The element specific magnetic moment per Co atom is found to agree well with the theoretical calculation, while that per Fe atom is decreased. By substituting the Fe with Cr atoms, Co2sCr,FedAl films can preserve these ideal properties and can show half metallicity at room temperature. [ABSTRACT FROM AUTHOR]

We grew Co2(Cr1-xFex)Al Heusler alloy films using a magnetron sputtering system on thermally oxidized Si substrates at room temperature without any buffer layers. The x-ray diffraction patterns did not show the L21 structure as expected for the bulk but revealed the B2 and A2 structures, depending on the Fe concentration x, in which the structure tends to become the A2 with increasing x. The magnetic moment and the Curie temperature monotonically increased with increasing x. Spin-valve-type tunneling junctions consisting of Co2Cr1-xFexAl (100 nm)/AlOx (1.4 nm)/CoFe (3 nm)/NiFe (5 nm)/IrMn (15 nm)/Ta (10 nm) were fabricated on thermally oxidized Si substrates without any buffer layers using metal masks. The maximum tunneling magnetoresistance at room temperature was obtained as 19% for x=0.4. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]