Current distribution inside Py/Cu lateral spin-valve device

We have investigated experimentally the non-local voltage signal (NLVS) in the lateral permalloy (Py)/Cu/Py spin valve devices with different width of Cu stripes. We found that NLVS strongly depends on the distribution of the spin-polarized current inside Cu strip in the vicinity of the Py-detector. To explain these data we have developed a diffusion model describing spatial (3D) distribution of the spin-polarized current in the device. The results of our calculations show that NLVS is decreased by factor of 10 due to spin flip-scattering occurring at Py/Cu interface. The interface resistivity on Py/Cu interface is also present, but its contribution to reduction of NLVS is minor. We also found that most of the spin-polarized current is injected within the region 30 nm from Py-injector/Cu interface. In the area at Py-detector/Cu interface, the spin-polarized current is found to flow mainly close on the injector side, with 1/e exponential decay in the magnitude within the distance 80 nm.Comment: 10 pages, 14 figure

Suppression of Giant Magnetoresistance by a superconducting contact

We predict that current perpendicular to the plane (CPP) giant magnetoresistance (GMR) in a phase-coherent magnetic multilayer is suppressed when one of the contacts is superconducting. This is a consequence of a superconductivity-induced magneto-resistive (SMR) effect, whereby the conductance of the ferromagnetically aligned state is drastically reduced by superconductivity. To demonstrate this effect, we compute the GMR ratio of clean (Cu/Co)_nCu and (Cu/Co)_nPb multilayers, described by an ab-initio spd tight binding Hamiltonian. By analyzing a simpler model with two orbitals per site, we also show that the suppression survives in the presence of elastic scattering by impurities.Comment: 5 pages, 4 figures. Submitted to PR

Spin diffusion at finite electric and magnetic fields

Spin transport properties at finite electric and magnetic fields are studied by using the generalized semiclassical Boltzmann equation. It is found that the spin diffusion equation for non-equilibrium spin density and spin currents involves a number of length scales that explicitly depend on the electric and magnetic fields. The set of macroscopic equations can be used to address a broad range of the spin transport problems in magnetic multilayers as well as in semiconductor heterostructure. A specific example of spin injection into semiconductors at arbitrary electric and magnetic fields is illustrated

Spin injection and spin accumulation in all-metal mesoscopic spin valves

We study the electrical injection and detection of spin accumulation in lateral ferromagnetic metal-nonmagnetic metal-ferromagnetic metal (F/N/F) spin valve devices with transparent interfaces. Different ferromagnetic metals, permalloy (Py), cobalt (Co) and nickel (Ni), are used as electrical spin injectors and detectors. For the nonmagnetic metal both aluminium (Al) and copper (Cu) are used. Our multi-terminal geometry allows us to experimentally separate the spin valve effect from other magneto resistance signals such as the anomalous magneto resistance (AMR) and Hall effects. We find that the AMR contribution of the ferromagnetic contacts can dominate the amplitude of the spin valve effect, making it impossible to observe the spin valve effect in a 'conventional' measurement geometry. In a 'non local' spin valve measurement we are able to completely isolate the spin valve signal and observe clear spin accumulation signals at T=4.2 K as well as at room temperature (RT). For aluminum we obtain spin relaxation lengths (lambda_{sf}) of 1.2 mu m and 600 nm at T=4.2 K and RT respectively, whereas for copper we obtain 1.0 mu m and 350 nm. The spin relaxation times tau_{sf} in Al and Cu are compared with theory and results obtained from giant magneto resistance (GMR), conduction electron spin resonance (CESR), anti-weak localization and superconducting tunneling experiments. The spin valve signals generated by the Py electrodes (alpha_F lambda_F=0.5 [1.2] nm at RT [T=4.2 K]) are larger than the Co electrodes (alpha_F lambda_F=0.3 [0.7] nm at RT [T=4.2 K]), whereas for Ni (alpha_F lambda_F<0.3 nm at RT and T=4.2 K) no spin signal is observed. These values are compared to the results obtained from GMR experiments.Comment: 16 pages, 12 figures, submitted to PR

A novel carbon leaving group in the reaction of organometallic compounds with phosphine oxides

The reaction of diphenyl(methoxymethyl)phosphine oxide 1 with organometallic reagents was found to lead to substitution of the methoxymethyl group. The P-phenyl substituent showed a lower propensity to undergo a displacement

Tunneling Magnetoresistance in Ferromagnetic Junctions: Bias Dependence

Electron tunneling between two ferromagnetic electrodes across an insulating barrier is analysed theoretically and experimentally. The barrier is either uniform or it includes a layer of small magnetic metallic particles. Particular attention is paid to the origin of the tunneling magnetoresistance and its bias dependence, as well as to the effects due to Coulomb blockade

Holdup measurement for nuclear fuel manufacturing plants

The assay of nuclear material holdup in fuel manufacturing plants is a laborious but often necessary part of completing the material balance. A range of instruments, standards, and a methodology for assaying holdup has been developed. The objectives of holdup measurement are ascertaining the amount, distribution, and how firmly fixed the SNM is. The purposes are reconciliation of material unbalance during or after a manufacturing campaign or plant decommissioning, to decide security requirements, or whether further recovery efforts are justified

Py/Cu/Co/Cu spin-valve magnetoresistive multilayers with weak interlayer coupling

Lucinski T, Urbaniak M, Stobiecki F, Hütten A, Reiss G. Py/Cu/Co/Cu spin-valve magnetoresistive multilayers with weak interlayer coupling. In: Czechoslovak Journal of Physics. CZECHOSLOVAK JOURNAL OF PHYSICS. Vol 52. INST PHYSICS ACAD SCI CZECH REPUBLIC; 2002: A165-A168.The magnetoresistive properties of [NiFe/CuAgAu/Co/CuAgAu](N) multilayers are described. It is shown that these structures exhibit large resistance changes within a small magnetic field range. It leads to high GMR field sensitivities reaching 6.8%/Oe at room temperature. Magnetoresistance effect is anisotropic with the highest resistance changes being observed for field applied parallel to an easy axis of permalloy layers

Contactless magnetoresistance studies of Co/Cu multilayers using the infrared magnetorefractive effect

The magnetotransport properties of giant magnetoresistive Co∕Cu multilayers are studied with the magnetorefractive effect: a noncontact technique, which uses infrared electromagnetic radiation. Four Co∕Cu samples were analyzed with the structure (Co15.5 Å∕Cux)25 which exhibit magnetoresistance values from 1.9 to 65 %. The magnetorefractive curves were modeled using the complex dielectric function as derived by Jacquet and Valet [J. C. Jacquet and T. Valet, Magnetic Ultrathin Films, Multilayer and Surfaces, edited by E. Marinero (Materials Research Society, Pittsburgh, 1995)]. The shape and magnitude of the curves were found to be very sensitive to the interface scattering lifetime. This classical model is successful in simulating the long wavelength behavior, but is not able to reproduce the correct shape or sign at short wavelengths where the band structure of the materials becomes important. The good agreement at long wavelengths between electrical magnetotransport measurements and the noncontact magnetorefractive effect demonstrates the possibilities of using infrared reflection spectroscopy for the characterization of giant magnetoresistive systems