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The magnetorefractive effect (MRE) has become an established technique for the contactless measurement of giant and colossal magnetoresistance and has also been extended to the study of thick granular tunnelling films. Here, the MRE is used to study the behaviour of a MgO(100)/Mg0(20 nm)/Fe(20 nm)/MgO(1.5 nm)/Fe(5 nm)/Co(3 nm)/Au(3 nm) magnetic tunnel junction patterned into square pillars of lateral dimension: 50/[micro]m and 5 [micro]m. A significant MRE is observed, enhanced by the presence of an absorption edge associated with MgO, although the exact origin of the effect is unclear. Index Terms--Infrared, magnetoresistance, tunnelling.

Microstructures and magnetic domain structures of nano-granular CoPt-Al-O thin films are investigated by Lorentz microscopy and electrum holography. It is found that the CoPt-based nanocrystalline phases are basically surrounded by the [Al.sub.2][O.sub.3]-based amorphous phases and the area of the [Al.sub.2][O.sub.3]-based amorphous phases increases with the increase in oxygen content. Typical mazy domains and domain walls like fishbone are observed in the [Co.sub.45.8][Pt.sub.18.6][Al.sub.17.3][O.sub.18.3] and in localized area of the [Co.sub.38.7][Pt.sub.15.6][Al.sub.16.3][O.sub.29.4], respectively, while no magnetic domain walls are observed in the [Co.sub.34.4][Pt.sub.13.5][Al.sub.15.6][O.sub.36.5]. With the increase in magnetic field, domain walls like fishbone start to disappear and the magnetic flux density increases in the [Co.sub.38.7][Pt.sub.15.6][Al.sub.16.3][O.sub.29.4], indicating the mixed-phase slate of ferromagnetic and superparamagnetic phases. In the [Co.sub.34.4][Pt.sub.13.5][Al.sub.15.6][O.sub.36.5] of superparamagnetic state, the fluctuated lines of magnetic flux are considered to reflect the randomly magnetized distribution of CoPt-based single domain particles. Index Terms--Electron holography, lines of magnetic flux, magnetic domain structure, nano-granular thin film.

Magnetic tunnel junctions (MTJs) with an L[1.sub.0]-ordered FePt alloy were fabricated and characterized. As a bottom electrode, an in-plane magnetized L[1.sub.0] FePt(110) layer was grown epitaxially on an Au buffer layer. A multiple oxidation process was used for the formation of Al oxide barriers. The L[1.sub.0]-FePt/AlO/FeCo MTJ prepared shows tunnel magnetoresistance of 18% and 40% at room temperature (RT) and 4.2 K, respectively. The observed RT magnetoresistance is improved, compared to the previously reported results for the L[1.sub.0]-FePt MTJs by a conventional single oxidation process. Index Terms--FePt-ordered alloy, multiple oxidation, tunnel junction, tunnel magnetoresistance.

Heusler alloy-based lateral spin valves with ohmic contacts are prepared for the Co2Fe Ga0.5Ge0.5)/Cu system by means of the top-down microfabrication process. The magneto-transport and microstructure are characterized to investigate the influence of the microfabrication route on the spin dependent transport of lateral spin valves systematically. A large non-local spin signa (%#916;RS) of 17.3mΩ is observed at room temperature, which is attributed to the highly spin-polarized Co2Fe(Ga0.5Ge0.5) ferromagnet and the clean Co2Fe(Ga0.5Ge0.5)/Cu interfaces confirmed by transmission electron microscopy. Based on the general expression of one-dimensional spin diffusion model, we discuss the importance of interfacial spin polarization in Heusler alloy-based [ABSTRACT FROM AUTHOR]

Magnetic domain structures and perpendicular magnetic anisotropies for [L1.sub.0]-ordered FePt alloy films have been investigated. The films were prepared by alternating Fe (001) and Pt (001) monatomic layers on MgO (001) substrates at low temperatures below 230[degrees]C. In addition to the fundamental (002) peak, (001) and (003) superlattice peaks have clearly been observed in the X-ray diffraction patterns, indicating the formation of [L1.sub.0]-ordered structure. The magnetization measurements show that all the samples are perpendicularly magnetized. Good magnetic squareness (Mr/Ms~0.9) from the magnetization curves are obtained and highly interconnected stripe domain patterns are observed for the samples grown at Ts [greater than or equal to] 160[degrees]C. Index Terms--Domain structure, FePt alloy, [L1.sub.0]-ordered structure, monatomic layer deposition, perpendicular magnetic anisotropy.

A study was conducted to analyze the magnetic characteristics of (Co(sub 1-x)Fe(sub x))-Al-O granular thin films prepared by a reactive sputtering technique under an atmosphere of O2 + Ar. The photoresist films were coated onto the magnetic film and heated in the range 100 to 300 degrees C. Experimental results indicated that the granular films supported the same general tendency as bulk Co-Fe alloys in the compositional dependence of magnetostriction.

The temperature and bias-voltage dependence of tunnel-type giant magnetoresistance (MR) in insulating granular films Co-A1-0. At low temperatures, enhancement of MR larger than the theoretical value, was observed, decreasing sharply with increasing temperature. MR did not decrease with rising bias voltage. The effect of temperature was different from that of bias voltage.

Magnetic properties of [001]-oriented L10 FePt1-xRhx films (tFePtRh=6.12 nm) with Rh composition (x) of 0≤x≤0.40 were studied, and the magnetic phase in a composition-temperature plane was investigated. At room temperature, the films with 0≤x≤0.32 were in a ferromagnetic (FM) phase with a coercivity of several kilo-oersteds, and the films with 0.34≤x≤0.40 were in an antiferromagnetic (AF) phase. At x=0.32, which is close to the critical composition of the FM-AF transition at room temperature, the uniaxial magnetocrystalline anisotropy (Ku) was about 1.7×107 erg/cm3. A bit patterning process using the discontinuous FM-AF transition was studied. First, microfabricated FePt square films (1.7 nm thick) were prepared on the AF FePt0.64Rh0.36 film (6.7 nm thick). Second, those square films and the FePt0.64Rh0.36 film were mixed by annealing. The Fe and Pt atoms were thermally diffused into the FePt0.64Rh0.36 film locally, and the composition of the diffused areas changed to FM FePt0.72Rh0.28. A magnetic force microscopy study suggested that only the diffused areas changed from AF to FM phase. A minimum FM dot size of 300×300 nm2 was realized, and the FM dots were multidomain structures. [ABSTRACT FROM AUTHOR]

Effects of porosity and pore orientation on the magnetization process were studied for lotus-type porous nickel and cobalt. It was confirmed that the saturation magnetization of porous metals varied linearly with the porosity, independent of the pore growth directions. Anisotropic behavior was clearly observed for the magnetization curves of lotus-type porous nickel, i.e., the magnetization perpendicular to the pore growth direction is always smaller than that parallel to the pore growth direction. The observed anisotropy is significantly large in the low magnetic field range below 2.5 kOe and is attributed to the anisotropic forms of the pores. Furthermore, it was found that the porosity dependence of magnetization at a certain applied field can be expressed by the empirical formula called Archie’s law, and the values of their exponents in the parallel and perpendicular directions at around 200 Oe were determined to be 1.1 and 1.8, respectively. These values are coincident with those reported for electrical conductivity of lotus-type porous nickel in the parallel and perpendicular directions. [ABSTRACT FROM AUTHOR]

We have investigated transport properties of carriers excited in high-quality homoepitaxial diamond (100) films by 5.6 eV photons or 15 keV electrons. The high-quality single-crystalline diamond films were homoepitaxially grown on type-Ib diamond substrates at a rate of 2.5 μm/h by high-power microwave-plasma chemical-vapor-deposition (MPCVD). In cathodoluminescence (CL) measurements, strong free-exciton recombination emissions were observed at room temperature from the almost whole specimen surface, indicating the grown films have substantially high quality. It is found through an analysis of the visible emission band originating from the type-Ib substrate that decay constants estimated for excited carriers were ∼5 μm in the depth direction. This is consistent with the fact that the intensity of spotlike CL images varied with an exponential function of the lateral length. From transient photocurrent measurements using ultrashort pulse laser excitations, decay times τ for the present high-quality diamond were estimated to be 15 and 100 ns for electrons and holes, respectively. Charge collection distances at an electric field E of 830 V/cm were deduced to be ∼190 μm and over 1.2 mm for electrons and holes, respectively. The former may give a high electron drift mobility of μ∼1600 cm2/Vs while the diffusion coefficients estimated for electrons are 55±14 cm2/V s, which is comparable with or even higher than those of Si. These physical quantities demonstrate high quality of the diamond films grown by means of the high-power MPCVD method. [ABSTRACT FROM AUTHOR]

The effect of high magnetic field on the microstructure and magnetic properties of α[sup ′]-FeN films has been studied. The application of a high magnetic field during sputter deposition has a significant influence on the microstructure of α[sup ′]-FeN films. In particular, the grain growth and the surface roughness are suppressed, and concurrently the coercivity becomes much lower. α[sup ′]-FeN films deposited in magnetic fields of 2 and 4 T exhibit smooth surfaces with root-mean-square (rms) roughness of, respectively, 0.38–1.53 nm, saturation magnetization of 2.25–2.32 T and coercivity of 1.6–2.6 kA/m, while α[sup ′]-FeN films deposited at H=0 T show rough surfaces with rms roughness of 6.0–6.8 nm, saturation magnetization of 2.13–2.15 T and coercivity of 9.8–12 kA/m. This effect of high magnetic field on the surface morphology is expected to be widely used to improve various properties of thin films. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The studies related to the magnetic properties of [001]-oriented [L1.sub.0]Fe[Pt.sub.1-x][Rh.sub.x] films ([t.sub.FePtRh]=6.12 nm) with Rh composition (x) of 0 [less than equal to] x [less than equal to] 0.40 and the magnetic phase in a composition-temperature plane are presented. The films with 0 [less than equal to] x [less than equal to] 0.32, at room temperature showed a ferromagnetic (FM) phase with a coercivity of several kilo-oersteds, and the films with 0.34 [less than equal to] x [less than equal to] 0.40 are found to be in an antiferromagnetic (AF) phase.

The space layer thickness dependence of interlayer exchange coupling is examined in the fully epitaxial trilayers of the [Co.sub.2]MnAl (CMA)/Cr/CMA structure. The comparison of the results of the experiments and the simulations of magnetization curves have disclosed novel behavior, dominating the 90[degree] coupling and the absence of 180[degree] coupling.

The magnetization process of epitaxial [Co.sub.2]MnSi/Cr/[Co.sub.2]MnSi trilayers with oscillatory interlayer exchange coupling is investigated. The 90 degree Celsiusoupling energy and the anisotropy constant has disclosed that the strength of 90 degree Celsiusoupling decreases exponentially with the spacer layer thickness.

FePt/Au/FePt nanopillars with current-perpendicular-to-plane geometries are fabricated, and current induced magnetization switching is demonstrated. Resistance measured with sweeping current show the resistance change due to the change of the magnetization alignment of the two FePt layers, which is interpreted as the magnetization switching by spin-polarized current.