970 research outputs found
Magnetization reversal in the anisotropy-dominated regime using time-dependent magnetic fields
We study magnetization reversal using various r.f. magnetic pulses. We show
numerically that switching is possible with simple sinusoidal pulses; however
the optimum approach is to use a frequency-swept (chirped) r.f. magnetic pulse,
the shape of which can be derived analytically. Switching times of the order of
nanoseconds can be achieved with relatively small r.f. fields, independent of
the anisotropy's strength
Albedos and diameters of three Mars Trojan asteroids
We observed the Mars Trojan asteroids (5261) Eureka and (101429) 1998 VF31
and the candidate Mars Trojan 2001 FR127 at 11.2 and 18.1 microns using
Michelle on the Gemini North telescope. We derive diameters of 1.28, 0.78, and
<0.52 km, respectively, with corresponding geometric visible albedos of 0.39,
0.32, and >0.14. The albedos for Eureka and 1998 VF31 are consistent with the
taxonomic classes and compositions (S(I)/angritic and S(VII)/achrondritic,
respectively) and implied histories presented in a companion paper by Rivkin et
al. Eureka's surface likely has a relatively high thermal inertia, implying a
thin regolith that is consistent with predictions and the small size that we
derive.Comment: Icarus, in press. See companion paper 0709.1925 by Rivkin et al; two
minor typos fixe
Resonant switching using spin valves
Using micromagnetics we demonstrate that the r.f. field produced by a spin
valve can be used to reverse the magnetization in a magnetic nanoparticle. The
r.f. field is generated using a current that specifically excites a uniform
spin wave in the spin valve. This current is swept such that the
chirped-frequency generated by the valve matches the angular dependent resonant
frequency of the anisotropy-dominated magnetic nanoparticle, as a result of
which the magnetization reversal occurs. The switching is fast, requires
currents similar to those used in recent experiments with spin valves, and is
stable with respect to small perturbations. This phenomenon can potentially be
employed in magnetic information storage devices or recently discussed magnetic
computing schemes
Switching spin valves using r.f. currents
We show that magnetization reversal in spin-injection devices can be
significantly faster when using a chirped r.f. rather than d.c current pulse.
Alternatively one can use a simple sinusoidal r.f. pulse or an optimized series
of alternating, equal-amplitude, square pulses of varying width (a digitized
approximation to a chirped r.f. pulse) to produce switching using much smaller
currents than with a d.c. pulse.Comment: please disregard the previous versio
Continuous Neel to Bloch Transition as Thickness Increases: Statics and Dynamics
We analyze the properties of Neel and Bloch domain walls as a function of
film thickness h, for systems where, in addition to exchange, the dipole-dipole
interaction must be included. The Neel to Bloch phase transition is found to be
a second order transition at hc, mediated by a single unstable mode that
corresponds to oscillatory motion of the domain wall center. A uniform
out-of-plane rf-field couples strongly to this critical mode only in the Neel
phase. An analytical Landau theory shows that the critical mode frequency
varies as the square root of (hc - h) just below the transition, as found
numerically.Comment: 4 pages, 4 figure
Analytical and micromagnetic study of a Neel domain wall
Journals published by the American Physical Society can be found at http://journals.aps.org/For ferromagnets with exchange, dipolar interaction, and uniaxial anisotropy, by both analytic methods and micromagnetic simulations we study Neel domain walls in thin ferromagnetic strips of finite width. Comparison of the numerical results with the analytics yields parameter values that had been unspecified by the analytics, and determines the modifications needed to describe the magnetization both near the strip center and near the boundaries. With no uniaxial anisotropy, the domain wall center can be described by the same hyperbolic secant form as with uniaxial anisotropy, but the effective anisotropy constant must now be thought of as increasing with increasing film thickness and decreasing with increasing film width
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
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