248 research outputs found
The Intrinsic Magnetization of Antiferromagnetic Textures
Antiferromagnets (AFMs) exhibit intrinsic magnetization when the order
parameter spatially varies. This intrinsic spin is present even at equilibrium
and can be interpreted as a twisting of the homogeneous AFM into a state with a
finite spin. Because magnetic moments couple directly to external magnetic
fields, the intrinsic magnetization can alter the dynamics of antiferromagnetic
textures under such influence. Starting from the discrete Heisenberg model, we
derive the continuum limit of the free energy of AFMs in the exchange
approximation and explicitly rederive that the spatial variation of the
antiferromagnetic order parameter is associated with an intrinsic magnetization
density. We calculate the magnetization profile of a domain wall and discuss
how the intrinsic magnetization reacts to external forces. We show
conclusively, both analytically and numerically, that a spatially inhomogeneous
magnetic field can move and control the position of domain walls in AFMs. By
comparing our model to a commonly used alternative parametrization procedure
for the continuum fields, we show that the physical interpretations of these
fields depend critically on the choice of parametrization procedure for the
discrete-to-continuous transition. This can explain why a significant amount of
recent studies of the dynamics of AFMs, including effective models that
describe the motion of antiferromagnetic domain walls, have neglected the
intrinsic spin of the textured order parameter.Comment: 12 pages, 7 figure
Staggered Dynamics in Antiferromagnets by Collective Coordinates
Antiferromagnets can be used to store and manipulate spin information, but
the coupled dynamics of the staggered field and the magnetization are very
complex. We present a theory which is conceptually much simpler and which uses
collective coordinates to describe staggered field dynamics in
antiferromagnetic textures. The theory includes effects from dissipation,
external magnetic fields, as well as reactive and dissipative current-induced
torques. We conclude that, at low frequencies and amplitudes, currents induce
collective motion by means of dissipative rather than reactive torques. The
dynamics of a one-dimensional domain wall, pinned at 90 at its ends,
are described as a driven harmonic oscillator with a natural frequency
inversely proportional to the length of the texture.Comment: 4 pages, 2 figure
Magnetic susceptibility of vanadium carbide
Magnetic susceptibility of vanadium carbide from 77 to 300 K measured by magnetomete
Gamma-widths, lifetimes and fluctuations in the nuclear quasi-continuum
Statistical -decay from highly excited states is determined by the
nuclear level density (NLD) and the -ray strength function
(SF). These average quantities have been measured for several nuclei
using the Oslo method. For the first time, we exploit the NLD and SF to
evaluate the -width in the energy region below the neutron binding
energy, often called the quasi-continuum region. The lifetimes of states in the
quasi-continuum are important benchmarks for a theoretical description of
nuclear structure and dynamics at high temperature. The lifetimes may also have
impact on reaction rates for the rapid neutron-capture process, now
demonstrated to take place in neutron star mergers.Comment: CGS16, Shanghai 2017, Proceedings, 5 pages, 3 figure
Scissors resonance in the quasi-continuum of Th, Pa and U isotopes
The gamma-ray strength function in the quasi-continuum has been measured for
231-233Th, 232,233Pa and 237-239U using the Oslo method. All eight nuclei show
a pronounced increase in gamma strength at omega_SR approx 2.4 MeV, which is
interpreted as the low-energy M1 scissors resonance (SR). The total strength is
found to be B_SR = 9-11 mu_N^2 when integrated over the 1 - 4 MeV gamma-energy
region. The SR displays a double-hump structure that is theoretically not
understood. Our results are compared with data from (gamma, gamma') experiments
and theoretical sum-rule estimates for a nuclear rigid-body moment of inertia.Comment: 11 pages, 9 figure
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