7 research outputs found
Magnetization reversal by injection and transfer of spin: experiments and theory
Reversing the magnetization of a ferromagnet by spin transfer from a current,
rather than by applying a magnetic field, is the central idea of an extensive
current research. After a review of our experiments of current-induced
magnetization reversal in Co/Cu/Co trilayered pillars, we present the model we
have worked out for the calculation of the current-induced torque and the
interpretation of the experiments
Micromagnetic simulations of absoption spectra
Further development of a previously introduced method for numerically
simulating magnetic spin waves is presented. Together with significant
improvements in speed, the method now allows one to calculate the energy
absorbed by the various modes excited by a position- and time-dependent H1
field in a ferromagnetic body of arbitrary shape in the presence of a (uniform
or non uniform) static H0 field as well as the internal exchange and anisotropy
fields. The method is applied to the case of the single vortex state in a thin
disc, a ring, and various square slabs, for which the absorption spectra are
calculated and the most strongly excited resonance modes are identified
Theory of Current-Induced Magnetization Precession
We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to
demonstrate that unpolarized current flow from a non-magnet into a ferromagnet
can produce a precession-type instability of the magnetization. The fundamental
origin of the instability is the difference in conductivity between majority
spins and minority spins in the ferromagnet. This leads to spin accumulation
and spin currents that carry angular momentum across the interface. The
component of this angular momentum perpendicular to the magnetization drives
precessional motion that is opposed by Gilbert damping. Neglecting magnetic
anisotropy and magnetostatics, our approximate analytic and exact numerical
solutions using realistic values for the material parameters show (for both
semi-infinite and thin film geometries) that a linear instability occurs when
both the current density and the excitation wave vector parallel to the
interface are neither too small nor too large. For many aspects of the problem,
the variation of the magnetization in the direction of the current flows makes
an important contribution.Comment: Submitted to Physical Review
Magnetic vortex oscillator driven by dc spin-polarized current
Transfer of angular momentum from a spin-polarized current to a ferromagnet
provides an efficient means to control the dynamics of nanomagnets. A peculiar
consequence of this spin-torque, the ability to induce persistent oscillations
of a nanomagnet by applying a dc current, has previously been reported only for
spatially uniform nanomagnets. Here we demonstrate that a quintessentially
nonuniform magnetic structure, a magnetic vortex, isolated within a nanoscale
spin valve structure, can be excited into persistent microwave-frequency
oscillations by a spin-polarized dc current. Comparison to micromagnetic
simulations leads to identification of the oscillations with a precession of
the vortex core. The oscillations, which can be obtained in essentially zero
magnetic field, exhibit linewidths that can be narrower than 300 kHz, making
these highly compact spin-torque vortex oscillator devices potential candidates
for microwave signal-processing applications, and a powerful new tool for
fundamental studies of vortex dynamics in magnetic nanostructures.Comment: 14 pages, 4 figure
SEAFP, Safety and Environmental Assessment of Fusion Power, Final Report
The Safety and Environmental Assessment of Fusion Power (SEAFP) was undertaken for the Commission of the European Union in the framework of the Fusion Programme 1990-94. Its terms of reference were in accordance with the programme decision of the Council of Ministers which followed a request by the European Parliament and a recommendation of the Fusion Programme Evaluation Board. The SEAFP is part of an ongoing effort to consider the safety and environmental aspects of fusion power. SEAFP was carried out by the NET Team, the Euratom/UKAEA Association, and by Industry, with contributions from other Associated Laboratories, the Joint Research Centre and the Canadian fusion programme