211 research outputs found
Spin switching in antiferromagnets using Neel-order spin-orbit torques
Antiferromagnets offer considerable potential for electronic device applications. This article reviews recent demonstrations of spin manipulation in antiferromagnetic devices using applied electrical currents. Due to spin-orbit coupling in environments with particular crystalline or structural symmetries, the electric current can induce an effective magnetic field with a sign that alternates on the lengthscale of the unit cell. The staggered effective field provides an efficient mechanism for switching antiferromagnetic domains and moving antiferromagnetic domain walls, with writing speeds in the terahertz regime
High quality GaMnAs films grown with As dimers
We demonstrate that GaMnAs films grown with As2 have excellent structural,
electrical and magnetic properties, comparable or better than similar films
grown with As4. Using As2, a Curie temperature of 112K has been achieved, which
is slightly higher than the best reported to date. More significantly, films
showing metallic conduction have been obtained over a much wider range of Mn
concentrations (from 1.5% to 8%) than has been reported for films grown with
As4. The improved properties of the films grown with As2 are related to the
lower concentration of antisite defects at the low growth temperatures
employed.Comment: 8 pages, accepted for publication in J. Crystal Growt
Domain Wall Resistance in Perpendicular (Ga,Mn)As: dependence on pinning
We have investigated the domain wall resistance for two types of domain walls
in a (Ga,Mn)As Hall bar with perpendicular magnetization. A sizeable positive
intrinsic DWR is inferred for domain walls that are pinned at an etching step,
which is quite consistent with earlier observations. However, much lower
intrinsic domain wall resistance is obtained when domain walls are formed by
pinning lines in unetched material. This indicates that the spin transport
across a domain wall is strongly influenced by the nature of the pinning.Comment: 9 pages, 3 figure
Structural characterisation of MBE grown zinc-blende Ga1-xMnxN/GaAs(001) as a function of Ga flux
Ga1-xMnxN films grown on semi-insulating GaAs(001) substrates at 680°C with fixed Mn flux and varied Ga flux demonstrated a transition from zinc-blende/wurtzite mixed phase growth for low Ga flux (N-rich conditions) to zinc-blende single phase growth with surface Ga droplets for high Ga flux (Ga-rich conditions). N-rich conditions were found favourable for Mn incorporation in GaN lattice. α-MnAs inclusions were identified extending into the GaAs buffer layer
Dephasing time of disordered two-dimensional electron gas in modulated magnetic fields
The dephasing time of disordered two-dimensional electron gas in a modulated
magnetic field is studied. It is shown that in the weak inhomogeneity limit,
the dephasing rate is proportional to the field amplitude, while in strong
inhomogeneity limit the dependence is quadratic. It is demonstrated that the
origin of the dependence of dephasing time on field amplitude lies in the
nature of corresponding single-particle motion. A semiclassical Monte Carlo
algorithm is developed to study the dephasing time, which is of qualitative
nature but efficient in uncovering the dependence of dephasing time on field
amplitude for arbitrarily complicated magnetic-field modulation. Computer
simulations support analytical results. The crossover from linear to quadratic
dependence is then generalized to the situation with magnetic field modulated
periodically in one direction with zero mean, and it is argued that this
crossover can be expected for a large class of modulated magnetic fields.Comment: 8 pages, 2 figure
Magnetic spin excitations in Mn doped GaAs : A model study
We provide a quantitative theoretical model study of the dynamical magnetic
properties of optimally annealed GaMnAs. This model has already
been shown to reproduce accurately the Curie temperatures for
GaMnAs. Here we show that the calculated spin stiffness are in
excellent agreement with those which were obtained from ab-initio based
studies. In addition, an overall good agreement is also found with available
experimental data. We have also evaluated the magnon density of states and the
typical density of states from which the "mobility edge", separating the
extended from localized magnon states, was determined. The power of the model
lies in its ability to be generalized for a broad class of diluted magnetic
semiconductor materials, thus it bridges the gap between first principle
calculations and model based studies.Comment: 5 pages, 5 figures, Text and some figures revised to match the
accepted versio
Effect of lithographically-induced strain relaxation on the magnetic domain configuration in microfabricated epitaxially grown Fe81Ga19
We investigate the role of lithographically-induced strain relaxation in a micron-scaled device fabricated from epitaxial thin films of the magnetostrictive alloy Fe81Ga19. The strain relaxation due to lithographic patterning induces a magnetic anisotropy that competes with the magnetocrystalline and shape induced anisotropy to play a crucial role in stabilising a flux-closing domain pattern. We use magnetic imaging, micromagnetic calculations and linear elastic modelling to investigate a region close to the edges of an etched structure. This highly-strained edge region has a significant influence on the magnetic domain configuration due to an induced magnetic anisotropy resulting from the inverse magnetostriction effect. We investigate the competition between the strain-induced and shape-induced anisotropy energies, and the resultant stable domain configurations, as the width of the bar is reduced to the nanoscale range. Understanding this behaviour will be important when designing hybrid magneto-electric spintronic devices based on highly magnetostrictive materials
Imaging current-induced switching of antiferromagnetic domains in CuMnAs
The magnetic order in antiferromagnetic materials is hard to control with external magnetic fields. Using X-ray Magnetic Linear Dichroism microscopy, we show that staggered effective fields generated by electrical current can induce modification of the antiferromagnetic domain structure in microdevices fabricated from a tetragonal CuMnAs thin film. A clear correlation between the average domain orientation and the anisotropy of the electrical resistance is demonstrated, with both showing reproducible switching in response to orthogonally applied current pulses. However, the behavior is inhomogeneous at the submicron level, highlighting the complex nature of the switching process in multi-domain antiferromagnetic films
Comparison of micromagnetic parameters of the ferromagnetic semiconductors (Ga,Mn)(As,P) and (Ga,Mn)As
We report on the determination of micromagnetic parameters of epilayers of the ferromagnetic semiconductor (Ga,Mn)As, which has an easy axis in the sample plane, and (Ga,Mn)(As,P), which has an easy axis perpendicular to the sample plane.We use an optical analog of ferromagnetic resonancewhere the laser-pulse-induced precession of magnetization is measured directly in the time domain. By the analysis of a single set of pump-and-probe magneto-optical data, we determined the magnetic anisotropy fields, the spin stiffness, and the Gilbert damping constant in these two materials. We show that incorporation of 10% of phosphorus in (Ga,Mn)As with 6% of manganese leads not only to the expected sign change of the perpendicular-to-plane anisotropy field but also to an increase of the Gilbert damping and to a reduction of the spin stiffness. The observed changes in the micromagnetic parameters upon incorporating P in (Ga,Mn)As are consistent with the reduced hole density, conductivity, and Curie temperature of the (Ga,Mn)(As,P) material.We also show that the apparent magnetization precession damping is stronger for the n=1 spinwave resonance mode than for the n=0 uniform magnetization precession mode
Magnetic susceptibilities of diluted magnetic semiconductors and anomalous Hall-voltage noise
The carrier spin and impurity spin densities in diluted magnetic
semiconductors are considered using a semiclassical approach. Equations of
motions for the spin densities and the carrier spin current density in the
paramagnetic phase are derived, exhibiting their coupled diffusive dynamics.
The dynamical spin susceptibilities are obtained from these equations. The
theory holds for p-type and n-type semiconductors doped with magnetic ions of
arbitrary spin quantum number. Spin-orbit coupling in the valence band is shown
to lead to anisotropic spin diffusion and to a suppression of the Curie
temperature in p-type materials. As an application we derive the Hall-voltage
noise in the paramagnetic phase. This quantity is critically enhanced close to
the Curie temperature due to the contribution from the anomalous Hall effect.Comment: 18 pages, 1 figure include
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