57 research outputs found
Current driven magnetization dynamics in ferromagnetic nanowires with Dzyaloshinskii-Moriya interaction
We study current induced magnetization dynamics in a long thin ferromagnetic
wire with Dzyaloshinskii-Moriya interaction (DMI). We find a spiral domain wall
configuration of the magnetization and obtain an analytical expression for the
width of the domain wall as a function of the interaction strengths. Our
findings show that above a certain value of DMI a domain wall configuration
cannot exist in the wire. Below this value we determine the domain wall
dynamics for small currents, and calculate the drift velocity of the domain
wall along the wire. We show that the DMI suppresses the minimum value of
current required to move the domain wall. Depending on its sign, the DMI
increases or decreases the domain wall drift velocity.Comment: 4 pages, 2 figure
Minimization of Ohmic losses for domain wall motion in a ferromagnetic nanowire
We study current-induced domain-wall motion in a narrow ferromagnetic wire.
We propose a way to move domain walls with a resonant time-dependent current
which dramatically decreases the Ohmic losses in the wire and allows to drive
the domain wall with higher speed without burning the wire. For any domain wall
velocity we find the time-dependence of the current needed to minimize the
Ohmic losses. Below a critical domain-wall velocity specified by the parameters
of the wire the minimal Ohmic losses are achieved by dc current. Furthermore,
we identify the wire parameters for which the losses reduction from its dc
value is the most dramatic.Comment: 4 pages (+ 4 pages of supplementary material), 4 figure
Electric signature of magnetic domain-wall dynamics
We study current-induced domain-wall dynamics in a thin ferromagnetic
nanowire. The domain-wall dynamics is described by simple equations with four
parameters. We propose the procedure to determine these parameters by
all-electric measurements of the time-dependent voltage induced by the
domain-wall motion. We provide an analytical expression for the time variation
of this voltage. Furthermore, we show that the measurement of the proposed
effects is within reach with current experimental techniques.Comment: 5 pages, 5 figures, update to published versio
Holey topological thermoelectrics
We study the thermoelectric properties of three-dimensional topological
insulators with many holes (or pores) in the bulk. We show that at high density
of these holes the thermoelectric figure of merit ZT can be large due to the
contribution of the conducting surfaces and the suppressed phonon thermal
conductivity. The maximum efficiency can be tuned by an induced gap in the
surface states dispersion through tunneling or external magnetic fields. The
large values of ZT, much higher than unity for reasonable parameters, make this
system a strong candidate for applications in heat management of nanodevices,
especially at low temperatures.Comment: 4+ pages, 6 figure
Engineering Curvature Induced Anisotropy in Thin Ferromagnetic Films
The large curvature effects on micromagnetic energy of a thin ferromagnetic
film with nonlocal dipolar energy are considered. We predict that the dipolar
interaction and surface curvature can produce perpendicular anisotropy which
can be controlled by engineering a special type of periodic surface shape
structure. Similar effects can be achieved by a significant surface roughness
in the film. We show that in general the anisotropy can point in an arbitrary
direction depending on the surface curvature. We provide simple examples of
these periodic surface structures to demonstrate how to engineer particular
anisotropies in the film.Comment: 5 pages, 4 figure
Multiscale Model Approach for Magnetization Dynamics Simulations
Simulations of magnetization dynamics in a multiscale environment enable
rapid evaluation of the Landau-Lifshitz-Gilbert equation in a mesoscopic sample
with nanoscopic accuracy in areas where such accuracy is required. We have
developed a multiscale magnetization dynamics simulation approach that can be
applied to large systems with spin structures that vary locally on small length
scales. To implement this, the conventional micromagnetic simulation framework
has been expanded to include a multiscale solving routine. The software
selectively simulates different regions of a ferromagnetic sample according to
the spin structures located within in order to employ a suitable discretization
and use either a micromagnetic or an atomistic model. To demonstrate the
validity of the multiscale approach, we simulate the spin wave transmission
across the regions simulated with the two different models and different
discretizations. We find that the interface between the regions is fully
transparent for spin waves with frequency lower than a certain threshold set by
the coarse scale micromagnetic model with no noticeable attenuation due to the
interface between the models. As a comparison to exact analytical theory, we
show that in a system with Dzyaloshinskii-Moriya interaction leading to spin
spiral, the simulated multiscale result is in good quantitative agreement with
the analytical calculation
Magnetoelectric domain wall dynamics and its implications for magnetoelectric memory
Domain wall dynamics in a magnetoelectric antiferromagnet is analyzed, and its implications for magnetoelectric memory applications are discussed. Cr2O3 is used in the estimates of the materials parameters. It is found that the domain wall mobility has a maximum as a function of the electric field due to the gyrotropic coupling induced by it. In Cr2O3, the maximal mobility of 0.1 m/(s Oe) is reached at E = 0.06 V/nm. Fields of this order may be too weak to overcome the intrinsic depinning field, which is estimated for B-doped Cr2O3. These major drawbacks for device implementation can be overcome by applying a small in-plane shear strain, which blocks the domain wall precession. Domain wall mobility of about 0.7 m/(s Oe) can then be achieved at E = 0.2 V/nm. A split-gate scheme is proposed for the domain-wall controlled bit element; its extension to multiple-gate linear arrays can offer advantages in memory density, programmability, and logic functionality
Walker solution for Dzyaloshinskii domain wall in ultrathin ferromagnetic films
We analyze the electric current and magnetic field driven domain wall motion
in perpendicularly magnetized ultrathin ferromagnetic films in the presence of
interfacial Dzyaloshinskii-Moriya interaction and both out-of-plane and
in-plane uniaxial anisotropies. We obtain exact analytical Walker-type
solutions in the form of one-dimensional domain walls moving with constant
velocity due to both spin-transfer torques and out-of-plane magnetic field.
These solutions are embedded into a larger family of propagating solutions
found numerically. Within the considered model, we find the dependencies of the
domain wall velocity on the material parameters and demonstrate that adding
in-plane anisotropy may produce domain walls moving with velocities in excess
of 500 m/s in realistic materials under moderate fields and currents.Comment: 6 pages, 2 figure
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