8,297 research outputs found
Domain wall motion in ferromagnetic nanowires driven by arbitrary time-dependent fields: An exact result
We address the dynamics of magnetic domain walls in ferromagnetic nanowires
under the influence of external time-dependent magnetic fields. We report a new
exact spatiotemporal solution of the Landau-Lifshitz-Gilbert equation for the
case of soft ferromagnetic wires and nanostructures with uniaxial anisotropy.
The solution holds for applied fields with arbitrary strength and time
dependence. We further extend this solution to applied fields slowly varying in
space and to multiple domain walls.Comment: 3 pages, 1 figur
Influence of band structure effects on domain-wall resistance in diluted ferromagnetic semiconductors
Intrinsic domain-wall resistance (DWR) in (Ga,Mn)As is studied theoretically
and compared to experimental results. The recently developed model of spin
transport in diluted ferromagnetic semiconductors [Van Dorpe et al., Phys. Rev.
B 72, 205322 (2005)] is employed. The model combines the disorder-free
Landauer-B\"uttiker formalism with the tight-binding description of the host
band structure. The obtained results show how much the spherical 4x4 kp model
[Nguyen, Shchelushkin, and Brataas, cond-mat/0601436] overestimates DWR in the
adiabatic limit, and reveal the dependence of DWR on the magnetization profile
and crystallographic orientation of the wall.Comment: 4 pages, 4 figures, submitted to Phys. Rev. B - Rapid Com
Surface Roughness Dominated Pinning Mechanism of Magnetic Vortices in Soft Ferromagnetic Films
Although pinning of domain walls in ferromagnets is ubiquitous, the absence
of an appropriate characterization tool has limited the ability to correlate
the physical and magnetic microstructures of ferromagnetic films with specific
pinning mechanisms. Here, we show that the pinning of a magnetic vortex, the
simplest possible domain structure in soft ferromagnets, is strongly correlated
with surface roughness, and we make a quantitative comparison of the pinning
energy and spatial range in films of various thickness. The results demonstrate
that thickness fluctuations on the lateral length scale of the vortex core
diameter, i.e. an effective roughness at a specific length scale, provides the
dominant pinning mechanism. We argue that this mechanism will be important in
virtually any soft ferromagnetic film.Comment: 4 figure
Nanoscale Zeeman localization of charge carriers in diluted magnetic semiconductor-permalloy hybrids
We investigate the possibility of charge carrier localization in magnetic
semiconductors due to the presence of a highly inhomogeneous external magnetic
field. As an example, we study in detail the properties of a magnetic
semiconductor-permalloy disk hybrid system. We find that the giant Zeeman
respose of the magnetic semiconductor in conjuction with the highly non-uniform
magnetic field created by the vortex state of a permalloy disk can lead to
Zeeman localized states at the interface of the two materials. These trapped
state are chiral, with chirality controlled by the orientation of the core
magnetization of the permalloy disk. We calculate the energy spectrum and the
eigenstates of these Zeeman localized states, and discuss their experimental
signatures in spectroscopic probes.Comment: 4 pages, 1 figur
Domain structure of epitaxial Co films with perpendicular anisotropy
Epitaxial hcp Cobalt films with pronounced c-axis texture have been prepared
by pulsed lased deposition (PLD) either directly onto Al2O3 (0001) single
crystal substrates or with an intermediate Ruthenium buffer layer. The crystal
structure and epitaxial growth relation was studied by XRD, pole figure
measurements and reciprocal space mapping. Detailed VSM analysis shows that the
perpendicular anisotropy of these highly textured Co films reaches the
magnetocrystalline anisotropy of hcp-Co single crystal material. Films were
prepared with thickness t of 20 nm < t < 100 nm to study the crossover from
in-plane magnetization to out-of-plane magnetization in detail. The analysis of
the periodic domain pattern observed by magnetic force microscopy allows to
determine the critical minimum thickness below which the domains adopt a pure
in-plane orientation. Above the critical thickness the width of the stripe
domains is evaluated as a function of the film thickness and compared with
domain theory. Especially the discrepancies at smallest film thicknesses show
that the system is in an intermediate state between in-plane and out-of-plane
domains, which is not described by existing analytical domain models
Phase diagram of magnetic domain walls in spin valve nano-stripes
We investigate numerically the transverse versus vortex phase diagram of
head-to-head domain walls in Co/Cu/Py spin valve nano-stripes (Py: Permalloy),
in which the Co layer is mostly single domain while the Py layer hosts the
domain wall. The range of stability of the transverse wall is shifted towards
larger thickness compared to single Py layers, due to a magnetostatic screening
effect between the two layers. An approached analytical scaling law is derived,
which reproduces faithfully the phase diagram.Comment: 4 page
Field-Driven Domain-Wall Dynamics in GaMnAs Films with Perpendicular Anisotropy
We combine magneto-optical imaging and a magnetic field pulse technique to
study domain wall dynamics in a ferromagnetic (Ga,Mn)As layer with
perpendicular easy axis. Contrary to ultrathin metallic layers, the depinning
field is found to be smaller than the Walker field, thereby allowing for the
observation of the steady and precessional flow regimes. The domain wall width
and damping parameters are determined self-consistently. The damping, 30 times
larger than the one deduced from ferromagnetic resonance, is shown to
essentially originate from the non-conservation of the magnetization modulus.
An unpredicted damping resonance and a dissipation regime associated with the
existence of horizontal Bloch lines are also revealed
On the scaling behaviour of cross-tie domain wall structures in patterned NiFe elements
The cross-tie domain wall structure in micrometre and sub-micrometre wide
patterned elements of NiFe, and a thickness range of 30 to 70nm, has been
studied by Lorentz microscopy. Whilst the basic geometry of the cross-tie
repeat units remains unchanged, their density increases when the cross-tie
length is constrained to be smaller than the value associated with a continuous
film. This occurs when element widths are sufficiently narrow or when the wall
is forced to move close to an edge under the action of an applied field. To a
very good approximation the cross-tie density scales with the inverse of the
distance between the main wall and the element edge. The experiments show that
in confined structures, the wall constantly modifies its form and that the need
to generate, and subsequently annihilate, extra vortex/anti-vortex pairs
constitutes an additional source of hysteresis.Comment: 4 pages, 5 figures, accepted for publication in Europhysics Letters
(EPL
X-ray photoelectron emission microscopy in combination with x-ray magnetic circular dichroism investigation of size effects on field-induced N\'eel-cap reversal
X-ray photoelectron emission microscopy in combination with x-ray magnetic
circular dichroism is used to investigate the influence of an applied magnetic
field on N\'eel caps (i.e., surface terminations of asymmetric Bloch walls).
Self-assembled micron-sized Fe(110) dots displaying a moderate distribution of
size and aspect ratios serve as model objects. Investigations of remanent
states after application of an applied field along the direction of N\'eel-cap
magnetization give clear evidence for the magnetization reversal of the N\'eel
caps around 120 mT, with a 20 mT dispersion. No clear correlation could be
found between the value of the reversal field and geometrical features of the
dots
Rotating vortex dipoles in ferromagnets
Vortex-antivortex pairs are localized excitations and have been found to be
spontaneously created in magnetic elements. In the case that the vortex and the
antivortex have opposite polarities the pair has a nonzero topological charge,
and it behaves as a rotating vortex dipole. We find theoretically, and confirm
numerically, the form of the energy as a function of the angular momentum of
the system and the associated rotation frequencies. We discuss the process of
annihilation of the pair which changes the topological charge of the system by
unity while its energy is monotonically decreasing. Such a change in the
topological charge affects profoundly the dynamics in the magnetic system. We
finally discuss the connection of our results with Bloch Points (BP) and the
implications for BP dynamics.Comment: 6 pages, 2 figure
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