292 research outputs found
Edge atoms effects on the perpendicular anisotropy of ultrathin magnetic layers
The present work reports experimental and theoretical results for
electrodeposited Co/Au(111) ultrathin layers with very specific magnetic
behavior. We show that the observed two peaks in the out-of-plane
magnetization versus deposition time variation could be explained by the
remarkably high perpendicular anisotropy of the perimeter atoms of low-
dimensional islands formed during the layer-by-layer growth, as compared to
that of the surface atoms. Our results indicate that it is possible to sustain
high anisotropy in very small grains without coming across the
superparamagnetic limit, opening excellent opportunities for materials
engineering
Comment on “Thickness dependence of exchange bias and coercivity in a ferromagnetic layer coupled with an antiferromagnetic layer” [J. Appl. Phys. 94, 2529 (2003)]
Hu, Jin, and Ma have proposed a theoretical investigation on the influence of the antiferromagnetic layer thickness on the magnetic properties of ferromagnetic/ antiferromagnetic bilayers [J. Appl. Phys. 94, 2529 (2003)], considering both the bilinear and biquadratic exchange couplings, and have claimed that from their formulas for the hysteresis loop displacement and coercivity many interesting conclusions can be extracted. Unfortunately, the mathematical procedure used to find the equilibrium of the system is based on inadequate stability conditions and has led to nonphysical results. More importantly, the simple phenomenological model, employed by the authors, is intrinsically not capable to give the antiferromagnetic layer thickness dependence of the magnetic properties of such exchange-coupled bilayers
Edge atoms effects on the perpendicular anisotropy of ultrathin magnetic layers
The present work reports experimental and theoretical results for electrodeposited Co/Au(111) ultrathin layers with very specific magnetic behavior. We show that the observed two peaks in the out-of-plane magnetization versus deposition time variation could be explained by the remarkably high perpendicular anisotropy of the perimeter atoms of low-dimensional islands formed during the layer-by-layer growth, as compared to that of the surface atoms. Our results indicate that it is possible to sustain high anisotropy in very small grains without coming across the superparamagnetic limit, opening excellent opportunities for materials engineering
Magnetoelectric effect and phase transitions in CuO in external magnetic fields
Apart from being so far the only known binary multiferroic compound, CuO has
a much higher transition temperature into the multiferroic state, 230 K, than
any other known material in which the electric polarization is induced by
spontaneous magnetic order, typically lower than 100 K. Although the
magnetically induced ferroelectricity of CuO is firmly established, no
magnetoelectric effect has been observed so far as direct crosstalk between
bulk magnetization and electric polarization counterparts. Here we demonstrate
that high magnetic fields of about 50 T are able to suppress the helical
modulation of the spins in the multiferroic phase and dramatically affect the
electric polarization. Furthermore, just below the spontaneous transition from
commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213
K, even modest magnetic fields induce a transition into the incommensurate
structure and then suppress it at higher field. Thus, remarkable hidden
magnetoelectric features are uncovered, establishing CuO as prototype
multiferroic with abundance of competitive magnetic interactions.Comment: 26 pages, 5 figure
Size effects in near-ultraviolet Raman spectra of few-nanometer-thick silicon-oninsulator nanofilms
We have fabricated Si-on-insulator (SOI) layers with a thickness h1 of a few nanometers and
examined them by Raman spectroscopy with 363.8 nm excitation. We have found that phonon and
electron confinement play important roles in SOI with h1<10 nm. We have confirmed that the
first-order longitudinal optical phonon Raman band displays size-induced major homogeneous
broadening due to phonon lifetime reduction as well as minor inhomogeneous broadening due to
wave vector relaxation (WVR), both kinds of broadening being independent of temperature. Due to
WVR, transverse acoustic (TA) phonons become Raman-active and give rise to a broad band in the
range of 100–200 cm 1. Another broad band appeared at 200–400 cm 1 in the spectrum of SOI is
attributed to the superposition of 1st order Raman scattering on longitudinal acoustic phonons and
2nd order scattering on TA phonons. Suppression of resonance-assisted 2-nd order Raman bands in
SOI spectra is explained by the electron-confinement-induced direct band gap enlargement compared
to bulk Si, which is confirmed by SOI reflection spectra. Published by AIP Publishing.
[http://dx.doi.org/10.1063/1.4947021
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