888 research outputs found
Unified description of bulk and interface-enhanced spin pumping
The dynamics of non-equilibrium spin accumulation generated in metals or
semiconductors by rf magnetic field pumping is treated within a diffusive
picture. The dc spin accumulation produced in a uniform system by a rotating
applied magnetic field or by a precessing magnetization of a weak ferromagnet
is in general given by a (small) fraction of hbar omega, where omega is the
rotation or precession frequency. With the addition of a neighboring,
field-free region and allowing for the diffusion of spins, the spin
accumulation is dramatically enhanced at the interface, saturating at the
universal value hbar omega in the limit of long spin relaxation time. This
effect can be maximized when the system dimensions are of the order of sqrt(2pi
D omega), where D is the diffusion constant. We compare our results to the
interface spin pumping theory of A. Brataas et al. [Phys. Rev. B 66, 060404(R)
(2002)]
On-chip detection of ferromagnetic resonance of a single submicron permalloy strip
We measured ferromagnetic resonance of a single submicron ferromagnetic
strip, embedded in an on-chip microwave transmission line device. The method
used is based on detection of the oscillating magnetic flux due to the
magnetization dynamics, with an inductive pick-up loop. The dependence of the
resonance frequency on applied static magnetic field agrees very well with the
Kittel formula, demonstrating that the uniform magnetization precession mode is
being driven
Large cone angle magnetization precession of an individual nanomagnet with dc electrical detection
We demonstrate on-chip resonant driving of large cone-angle magnetization
precession of an individual nanoscale permalloy element. Strong driving is
realized by locating the element in close proximity to the shorted end of a
coplanar strip waveguide, which generates a microwave magnetic field. We used a
microwave frequency modulation method to accurately measure resonant changes of
the dc anisotropic magnetoresistance. Precession cone angles up to are
determined with better than one degree of resolution. The resonance peak shape
is well-described by the Landau-Lifshitz-Gilbert equation
Microwave spectroscopy on magnetization reversal dynamics of nanomagnets with electronic detection
We demonstrate a detection method for microwave spectroscopy on magnetization
reversal dynamics of nanomagnets. Measurement of the nanomagnet anisotropic
magnetoresistance was used for probing how magnetization reversal is resonantly
enhanced by microwave magnetic fields. We used Co strips of 2 um x 130 nm x 40
nm, and microwave fields were applied via an on-chip coplanar wave guide. The
method was applied for demonstrating single domain-wall resonance, and studying
the role of resonant domain-wall dynamics in magnetization reversal
Electrical detection of spin pumping: dc voltage generated by ferromagnetic resonance at ferromagnet/nonmagnet contact
We describe electrical detection of spin pumping in metallic nanostructures.
In the spin pumping effect, a precessing ferromagnet attached to a normal-metal
acts as a pump of spin-polarized current, giving rise to a spin accumulation.
The resulting spin accumulation induces a backflow of spin current into the
ferromagnet and generates a dc voltage due to the spin dependent conductivities
of the ferromagnet. The magnitude of such voltage is proportional to the
spin-relaxation properties of the normal-metal. By using platinum as a contact
material we observe, in agreement with theory, that the voltage is
significantly reduced as compared to the case when aluminum was used.
Furtheremore, the effects of rectification between the circulating rf currents
and the magnetization precession of the ferromagnet are examined. Most
significantly, we show that using an improved layout device geometry these
effects can be minimized.Comment: 9 pages, 11 figure
Electrical detection of spin pumping due to the precessing magnetization of a single ferromagnet
We report direct electrical detection of spin pumping, using a lateral normal
metal/ferromagnet/normal metal device, where a single ferromagnet in
ferromagnetic resonance pumps spin polarized electrons into the normal metal,
resulting in spin accumulation. The resulting backflow of spin current into the
ferromagnet generates a d.c. voltage due to the spin dependent conductivities
of the ferromagnet. By comparing different contact materials (Al and /or Pt),
we find, in agreement with theory, that the spin related properties of the
normal metal dictate the magnitude of the d.c. voltage
Simulation of a fully coupled 3D glacial isostatic adjustment – ice sheet model for the Antarctic ice sheet over a glacial cycle
Glacial isostatic adjustment (GIA) has a stabilizing effect on the evolution of the Antarctic ice sheet by reducing the grounding line migration following ice melt. The timescale and strength of this feedback depends on the spatially varying viscosity of the Earth's mantle. Most studies assume a relatively long and laterally homogenous response time of the bedrock. However, the mantle viscosity is spatially variable, with a high mantle viscosity beneath East Antarctica and a low mantle viscosity beneath West Antarctica. For this study, we have developed a new method to couple a 3D GIA model and an ice sheet model to study the interaction between the solid Earth and the Antarctic ice sheet during the last glacial cycle. With this method, the ice sheet model and GIA model exchange ice thickness and bedrock elevation during a fully coupled transient experiment. The feedback effect is taken into account with a high temporal resolution, where the coupling time steps between the ice sheet and GIA model are 5000 years over the glaciation phase and vary between 500 and 1000 years over the deglaciation phase of the last glacial cycle. During each coupling time step, the bedrock elevation is adjusted at every ice sheet model time step, and the deformation is computed for a linearly changing ice load. We applied the method using the ice sheet model ANICE and a 3D GIA finite element model. We used results from a regional seismic model for Antarctica embedded in the global seismic model SMEAN2 to determine the patterns in the mantle viscosity. The results of simulations over the last glacial cycle show that differences in mantle viscosity of an order of magnitude can lead to differences in the grounding line position up to 700 km and to differences in ice thickness of the order of 2 km for the present day near the Ross Embayment. These results underline and quantify the importance of including local GIA feedback effects in ice sheet models when simulating the Antarctic ice sheet evolution over the last glacial cycle.</p
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