120 research outputs found
Magnetic patterning of (Ga,Mn)As by hydrogen passivation
We present an original method to magnetically pattern thin layers of
(Ga,Mn)As. It relies on local hydrogen passivation to significantly lower the
hole density, and thereby locally suppress the carrier-mediated ferromagnetic
phase. The sample surface is thus maintained continuous, and the minimal
structure size is of about 200 nm. In micron-sized ferromagnetic dots
fabricated by hydrogen passivation on perpendicularly magnetized layers, the
switching fields can be maintained closer to the continuous film coercivity,
compared to dots made by usual dry etch techniques
Macrospin limit and configurational anisotropy in nanoscale Permalloy triangles
In Permalloy submicron triangles, configurational anisotropy - a higher-order
form of shape anisotropy - yields three equivalent easy axes, imposed by the
structures' symmetry order. Supported by micromagnetic simulations, an
experimental method was devised to evaluate the nanostructure dimensions for
which a Stoner-Wohlfarth type of reversal could be used to describe this
particular magnetic anisotropy. In this regime, a straightforward procedure
using an in-plane rotating field allowed us to quantify experimentally the
six-fold anisotropy fields for triangles of different thicknesses and sizes
Acoustic solitons: A robust tool to investigate the generation and detection of ultrafast acoustic waves
International audienceSolitons are self-preserving traveling waves of great interest in nonlinear physics but hard to observe experimentally. In this report an experimental setup is designed to observe and characterize acoustic solitons in a GaAs(001) substrate. It is based on careful temperature control of the sample and an interferometric detection scheme. Ultrashort acoustic solitons, such as the one predicted by the Korteweg–de Vries equation, are observed and fully characterized. Their particlelike nature is clearly evidenced and their unique properties are thoroughly checked. The spatial averaging of the soliton wave front is shown to account for the differences between the theoretical and experimental soliton profile. It appears that ultrafast acoustic experiments provide a precise measurement of the soliton velocity. It allows for absolute calibration of the setup as well as the response function analysis of the detection layer. Moreover, the temporal distribution of the solitons is also analyzed with the help of the inverse scattering method. It shows how the initial acoustic pulse profile which gives birth to solitons after nonlinear propagation can be retrieved. Such investigations provide a new tool to probe transient properties of highly excited matter through the study of the emitted acoustic pulse after laser excitation
Field-induced domain wall propagation: beyond the one-dimensional model
We have investigated numerically the field-driven propagation of
perpendicularly magnetized ferromagnetic layers. It was then compared to the
historical one-dimensional domain wall (DW) propagation model widely used in
spintronics studies of magnetic nanostructures. In the particular regime of
layer thickness (h) of the order of the exchange length, anomalous velocity
peaks appear in the precessional regime, their shape and position shifting with
h. This has also been observed experimentally. Analyses of the simulations show
a distinct correlation between the curvature of the DW and the twist of the
magnetization vector within it, and the velocity peak. Associating a
phenomenological description of this twist with a four-coordinate DW
propagation model, we reproduce very well these kinks and show that they result
from the torque exerted by the stray field created by the domains on the
twisted magnetization. The position of the peaks is well predicted from the
DW's first flexural mode frequency, and depends strongly on the layer
thickness. Comparison of the proposed model to DW propagation data obtained on
dilute semiconductor ferromagnets GaMnAs and GaMnAsP sheds light on the origin
of the measured peaks
Effect of picosecond strain pulses on thin layers of the ferromagnetic semiconductor (Ga,Mn)(As,P)
The effect of picosecond acoustic strain pulses (ps-ASP) on a thin layer of
(Ga,Mn)As co-doped with phosphorus was probed using magneto-optical Kerr effect
(MOKE). A transient MOKE signal followed by low amplitude oscillations was
evidenced, with a strong dependence on applied magnetic field, temperature and
ps-ASP amplitude. Careful interferometric measurement of the layer's thickness
variation induced by the ps-ASP allowed us to model very accurately the
resulting signal, and interpret it as the strain modulated reflectivity
(differing for probe polarizations), independently from dynamic
magnetization effects.Comment: 6 pages, 5 figure
Coupling and induced depinning of magnetic domain walls in adjacent spin valve nanotracks
The magnetostatic interaction between magnetic domain walls (DWs) in adjacent
nanotracks has been shown to produce strong inter-DW coupling and mutual
pinning. In this paper, we have used electrical measurements of adjacent
spin-valve nanotracks to follow the positions of interacting DWs. We show that
the magnetostatic interaction between DWs causes not only mutual pinning, as
observed till now, but that a travelling DW can also induce the depinning of
DWs in near-by tracks. These effects may have great implications for some
proposed high density magnetic devices (e.g. racetrack memory, DW logic
circuits, or DW-based MRAM).Comment: The following article has been accepted by the Journal of Applied
Physic
Universal conductance fluctuations in epitaxial GaMnAs ferromagnets: structural and spin disorder
Mesoscopic transport measurements reveal a large effective phase coherence
length in epitaxial GaMnAs ferromagnets, contrary to usual 3d-metal
ferromagnets. Universal conductance fluctuations of single nanowires are
compared for epilayers with a tailored anisotropy. At large magnetic fields,
quantum interferences are due to structural disorder only, and an unusual
behavior related to hole-induced ferromagnetism is evidenced, for both quantum
interferences and decoherence. At small fields, phase coherence is shown to
persist down to zero field, even in presence of magnons, and an additional spin
disorder contribution to quantum interferences is observed under domain walls
nucleation.Comment: 15 pages, 4 figure
Magnetic properties and domain structure of (Ga,Mn)As films with perpendicular anisotropy
The ferromagnetism of a thin GaMnAs layer with a perpendicular easy
anisotropy axis is investigated by means of several techniques, that yield a
consistent set of data on the magnetic properties and the domain structure of
this diluted ferromagnetic semiconductor. The magnetic layer was grown under
tensile strain on a relaxed GaInAs buffer layer using a procedure that limits
the density of threading dislocations. Magnetometry, magneto-transport and
polar magneto-optical Kerr effect (PMOKE) measurements reveal the high quality
of this layer, in particular through its high Curie temperature (130 K) and
well-defined magnetic anisotropy. We show that magnetization reversal is
initiated from a limited number of nucleation centers and develops by easy
domain wall propagation. Furthermore, MOKE microscopy allowed us to
characterize in detail the magnetic domain structure. In particular we show
that domain shape and wall motion are very sensitive to some defects, which
prevents a periodic arrangement of the domains. We ascribed these defects to
threading dislocations emerging in the magnetic layer, inherent to the growth
mode on a relaxed buffer
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