13 research outputs found
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
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