21 research outputs found
Harmonic oscillator model for current- and field-driven magnetic vortices
In experiments the distinction between spin-torque and Oersted-field driven
magnetization dynamics is still an open problem. Here, the gyroscopic motion of
current- and field-driven magnetic vortices in small thin-film elements is
investigated by analytical calculations and by numerical simulations. It is
found that for small harmonic excitations the vortex core performs an
elliptical rotation around its equilibrium position. The global phase of the
rotation and the ratio between the semi-axes are determined by the frequency
and the amplitude of the Oersted field and the spin torque
Current-Driven Domain-Wall Dynamics in Curved Ferromagnetic Nanowires
The current-induced motion of a domain wall in a semicircle nanowire with
applied Zeeman field is investigated. Starting from a micromagnetic model we
derive an analytical solution which characterizes the domain-wall motion as a
harmonic oscillation. This solution relates the micromagnetic material
parameters with the dynamical characteristics of a harmonic oscillator, i.e.,
domain-wall mass, resonance frequency, damping constant, and force acting on
the wall. For wires with strong curvature the dipole moment of the wall as well
as its geometry influence the eigenmodes of the oscillator. Based on these
results we suggest experiments for the determination of material parameters
which otherwise are difficult to access. Numerical calculations confirm our
analytical solution and show its limitations
Weak localization and spin splitting in inversion layers on p-type InAs
We report on the magnetoconductivity of quasi two-dimensional electron
systems in inversion layers on p-type InAs single crystals. In low magnetic
fields pronounced features of weak localization and antilocalization are
observed. They are almost perfectly described by the theory of Iordanskii,
Lyanda-Geller and Pikus. This allows us to determine the spin splitting and the
Rashba parameter of the ground electric subband as a function of the electron
density.Comment: Accepted for publication in Phys. Rev. B, 4 page
Supercurrent-phase relationship of a Nb/InAs(2DES)/Nb Josephson junction in overlapping geometry
Superconductor/normal conductor/superconductor (SNS) Josephson junctions with
highly transparent interfaces are predicted to show significant deviations from
sinusoidal supercurrent-phase relationships (CPR) at low temperatures. We
investigate experimentally the CPR of a ballistic Nb/InAs(2DES)/Nb junction in
the temperature range from 1.3 K to 9 K using a modified Rifkin-Deaver method.
The CPR is obtained from the inductance of the phase-biased junction. Transport
measurements complement the investigation. At low temperatures, substantial
deviations of the CPR from conventional tunnel-junction behavior have been
observed. A theoretical model yielding good agreement to the data is presented.Comment: RevTex4, 4 pages including 3 figure
Proposal for a standard problem for micromagnetic simulations including spin-transfer torque
The spin-transfer torque between itinerant electrons and the magnetization in a ferromagnet is of fundamental interest for the applied physics community. To investigate the spin-transfer torque, powerful simulation tools are mandatory. We propose a micromagnetic standard problem includingthe spin-transfer torque that can be used for the validation and falsication of micromagnetic simulation tools. The work is based on the micromagnetic model extended by the spin-transfer torque in continuously varying magnetizations as proposed by Zhang and Li. The standard problem geometry is a permalloy cuboid of 100 nm edge length and 10 nm thickness, which contains a Landau pattern with a vortex in the center of the structure. A spin-polarized dc current density of 1012 A/m2 flows laterally through the cuboid and moves the vortex core to a new steady-state position. We show that the new vortex-core position is a sensitive measure for the correctness of micromagnetic simulatorsthat include the spin-transfer torque. The suitability of the proposed problem as a standard problem is tested by numerical results from four different finite-difference and finite-element-based simulation tools