11,989 research outputs found
Emergence of skyrmion lattices and bimerons in chiral magnetic thin films with nonmagnetic impurities
Skyrmions are topologically protected field structures with particlelike characteristics that play important roles in several areas of science. Recently, skyrmions have been directly observed in chiral magnets. Here, we investigate the effects of pointlike nonmagnetic impurities on the distinct initial states (random or helical ones) and on the formation of the skyrmion crystal in a discrete lattice. Using Monte Carlo techniques, we have found that even a small percentage of spin vacancies present in the chiral magnetic thin film considerably affects the skyrmion order. The main effects of impurities are somewhat similar to thermal effects. The presence of these spin vacancies also induces the formation of bimerons in both the helical and skyrmion states. We also investigate how adjacent impurities forming a hole affect the skyrmion crystal
Magnetization reversals in a disk-shaped small magnet with an interface
We consider a nanodisk possessing two coupled materials with different
ferromagnetic exchange constant. The common border line of the two media passes
at the disk center dividing the system exactly in two similar half-disks. The
vortex core motion crossing the interface is investigated with a simple
description based on a two-dimensional model which mimics a very thin real
material with such a line defect. The main result of this study is that,
depending on the magnetic coupling which connects the media, the vortex core
can be dramatically and repeatedly flipped from up to down and vice versa by
the interface. This phenomenon produces burst-like emission of spin waves each
time the switching process takes place.Comment: 11 pages, 10 figure
Magnetic monopole and string excitations in a two-dimensional spin ice
We study the magnetic excitations of a square lattice spin-ice recently
produced in an artificial form, as an array of nanoscale magnets. Our analysis,
based upon the dipolar interaction between the nanomagnetic islands, correctly
reproduces the ground-state observed experimentally. In addition, we find
magnetic monopole-like excitations effectively interacting by means of the
usual Coulombic plus a linear confining potential, the latter being related to
a string-like excitation binding the monopoles pairs, what indicates that the
fractionalization of magnetic dipoles may not be so easy in two dimensions.
These findings contrast this material with the three-dimensional analogue,
where such monopoles experience only the Coulombic interaction. We discuss,
however, two entropic effects that affect the monopole interactions: firstly,
the string configurational entropy may loose the string tension and then, free
magnetic monopoles should also be found in lower dimensional spin ices;
secondly, in contrast to the string configurational entropy, an entropically
driven Coulomb force, which increases with temperature, has the opposite effect
of confining the magnetic defects.Comment: 8 pages. Accepted by Journal of Applied Physics (2009
Prediction of genetic potential of common bean segregant populations for slow seed-coat darkening.
The objective of this study was to predict the genetic potential of common bean segregant populations for slow seed-coat darkening
A espectroscopia fotoacústica como técnica para o monitoramento do processo de compostagem.
bitstream/CNPDIA-2010/12634/1/CT108-2009.pd
Uso da espectroscopia fotoacústica no processo de compostagem de poda de árvore associada a materiais da agroindústria.
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