123 research outputs found
Near-Boundary and Bulk Regions of a Semi-Infinite Two-Dimensional Heisenberg Antiferromagnet
Using the spin-wave approximation elementary excitations of a semi-infinite
two-dimensional Heisenberg antiferromagnet are considered. The
spectrum consists of bulk modes -- standing spin waves and a
quasi-one-dimensional mode of boundary spin waves. These latter excitations
eject bulk modes from two boundary rows of sites, thereby dividing the
antiferromagnet into two regions with different dominant excitations. As a
result absolute values of nearest-neighbor spin correlations on the edge exceed
the bulk value.Comment: 8 pages, 3 figure
Striped phases in two dimensional dipole systems
We prove that a system of discrete 2D in-plane dipoles with four possible
orientations, interacting via a 3D dipole-dipole interaction plus a nearest
neighbor ferromagnetic term, has periodic striped ground states. As the
strength of the ferromagnetic term is increased, the size of the stripes in the
ground state increases, becoming infinite, i.e., giving a ferromagentic ground
state, when the ferromagentic interaction exceeds a certain critical value. We
also give a rigorous proof of the reorientation transition in the ground state
of a 2D system of discrete dipoles with six possible orientations, interacting
via a 3D dipole-dipole interaction plus a nearest neighbor antiferromagnetic
term. As the strength of the antiferromagnetic term is increased the ground
state flips from being striped and in-plane to being staggered and
out-of-plane. An example of a rotator model with a sinusoidal ground state is
also discussed.Comment: 20 pages, 1 figur
Magnetostrictive hysteresis of TbCo/CoFe multilayers and magnetic domains
Magnetic and magnetostrictive hysteresis loops of TbCo/CoFe multilayers under
field applied along the hard magnetization axis are studied using vectorial
magnetization measurements, optical deflectometry and magneto optical Kerr
microscopy. Even a very small angle misalignment between hard axis and magnetic
field direction is shown to drastically change the shape of magnetization and
magnetostrictive torsion hysteresis loops. Two kinds of magnetic domains are
revealed during the magnetization: big regions with opposite rotation of
spontaneous magnetization vector and spontaneous magnetic domains which appear
in a narrow field interval and provide an inversion of this rotation.
We show that the details of the hysteresis loops of our exchange-coupled
films can be described using the classical model of homogeneous magnetization
rotation of single uniaxial films and the configuration of observed domains.
The understanding of these features is crucial for applications (for MEMS or
microactuators) which benefit from the greatly enhanced sensitivity near the
point of magnetic saturation at the transverse applied field.Comment: 10 pages, 11 figure
The Application of Multispectral Techniques to Analytical Electron Microscopy
The York multispectral analytical electron microscope (MULSAM) was the first instrument specifically designed to acquire and process multiple Auger, X-ray, backscattered electron, elastically scattered electron, scanning electron microscopy (SEM) and specimen absorption current images simultaneously. Analyzing combinations of these signals with multispectral correlation techniques yields more information than would normally be obtained by treating each image separately. This paper reports some of the multispectral methods we have investigated at York which may be of use to other workers. Included are (1) a method that corrects for beam current fluctuations during long acquisition runs which is based on the anti-correlation between SEM and specimen current images, (2) the classification of topography for crystalline specimens by correlation partitioning of backscattered electron images and (3) the enhancement of surface state contrast in multi spectral scanning tunneling microscopy (STM) images using the Hotelling transform. The last example is intended to demonstrate that these techniques can also be applied to other fields in microscopy
The soil electric potential signature of summer drought
During the period from late April to early August, a timeseries of soil electric potential measurements in the upper 15 cm of mineral soil were collected daily at the University of Michigan Botanical Gardens using an automatic data collection system. These data, after conversion to a surrogate measure of electrolyte concentration, provide a unique record of the 1988 summer drought in a continental location. The effects of rainfall-dewfall electrolyte dilution, evaporation-induced electrolyte concentration and upward-downward soil water advection are well-illustrated in the data. These observations demonstrate that soil electric potential is an easily measured variable of high information content, especially when collected with other system-linked environmental data.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41671/1/704_2004_Article_BF00866203.pd
Formation and coarsening of Ag(110) bilayer islands on NiAl(110): STM analysis and atomistic lattice-gas modeling
A Phase-Partitioning Model for CO2–Brine Mixtures at Elevated Temperatures and Pressures: Application to CO2-Enhanced Geothermal Systems
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