870 research outputs found
Regulating in the Shadow of the U.C.C.: How Courts Should Interpret State Consumer Protection Laws
Hysteresis and noise in ferromagnetic materials with parallel domain walls
We investigate dynamic hysteresis and Barkhausen noise in ferromagnetic
materials with a huge number of parallel and rigid Bloch domain walls.
Considering a disordered ferromagnetic system with strong in-plane uniaxial
anisotropy and in-plane magnetization driven by an external magnetic field, we
calculate the equations of motion for a set of coupled domain walls,
considering the effects of the long-range dipolar interactions and disorder. We
derive analytically an expression for the magnetic susceptivity, related to the
effective demagnetizing factor, and show that it has a logarithmic dependence
on the number of domains. Next, we simulate the equations of motion and study
the effect of the external field frequency and the disorder on the hysteresis
and noise properties. The dynamic hysteresis is very well explained by means of
the loss separation theory.Comment: 13 pages, 11 figure
The German Inflation Trauma
The notion of a nation-specific inflation trauma among the German population is ubiquitous in the public debate in Germany and beyond. Because of its experience with hyperinflation in 1923, the German population fears rising prices and favors stability-oriented monetary as well as fiscal policy. It is less clear, however, whether this contemporary understanding of the German inflation trauma is as old as its historical point of reference. The majority of the literature presumes that such a traumatic disposition has persisted since 1923 and has been transposed intergenerationally (persistence thesis). Others, however, point to an ex-ante reconstruction of past experiences (reconstruction thesis). By employing an interdisciplinary approach of methodological triangulation drawing on both methods of history and political sciences, we provide new insights on the question of origin. Specifically, we examine the remembrance of hyperinflation in personal memoirs and the German Bundestag in regard to the monetary and fiscal policy lessons connected to memories of 1923. Doing so, we find support for the logic of reconstruction. We show that the hyperinflation was not remembered unambiguously, and that memories were not immediately linked to specific policy lessons. Only from the 1980s onwards, a process of discursive alignment occurred that mirrors the contemporary understanding of the inflation trauma. By providing this insight, our paper allows to better understand the historical origins of today’s popular memory and its political uses.Not Reviewe
Mechanism for nonequilibrium symmetry breaking and pattern formation in magnetic films
Magnetic thin films exhibit a strong variation in properties depending on
their degree of disorder. Recent coherent x-ray speckle experiments on magnetic
films have measured the loss of correlation between configurations at opposite
fields and at the same field, upon repeated field cycling. We perform finite
temperature numerical simulations on these systems that provide a comprehensive
explanation for the experimental results. The simulations demonstrate, in
accordance with experiments, that the memory of configurations increases with
film disorder. We find that non-trivial microscopic differences exist between
the zero field spin configuration obtained by starting from a large positive
field and the zero field configuration starting at a large negative field. This
seemingly paradoxical beahvior is due to the nature of the vector spin dynamics
and is also seen in the experiments. For low disorder, there is an instability
which causes the spontaneous growth of line-like domains at a critical field,
also in accord with experiments. It is this unstable growth, which is highly
sensitive to thermal noise, that is responsible for the small correlation
between patterns under repeated cycling. The domain patterns, hysteresis loops,
and memory properties of our simulated systems match remarkably well with the
real experimental systems.Comment: 12 pages, 10 figures Added comparison of results with
cond-mat/0412461 and some more discussio
Effects of Domain Wall on Electronic Transport Properties in Mesoscopic Wire of Metallic Ferromagnets
We study the effect of the domain wall on electronic transport properties in
wire of ferromagnetic 3 transition metals based on the linear response
theory. We considered the exchange interaction between the conduction electron
and the magnetization, taking into account the scattering by impurities as
well. The effective electron-wall interaction is derived by use of a local
gauge transformation in the spin space. This interaction is treated
perturbatively to the second order. The conductivity contribution within the
classical (Boltzmann) transport theory turns out to be negligiblly small in
bulk magnets, due to a large thickness of the wall compared with the fermi
wavelength. It can be, however, significant in ballistic nanocontacts, as
indicated in recent experiments. We also discuss the quantum correction in
disordered case where the quantum coherence among electrons becomes important.
In such case of weak localization the wall can contribute to a decrease of
resistivity by causing dephasing. At lower temperature this effect grows and
can win over the classical contribution, in particular in wire of diameter
, being the inelastic diffusion
length. Conductance change of the quantum origin caused by the motion of the
wall is also discussed.Comment: 30 pages, 4 figures. Detailed paper of Phys. Rev. Lett. 78, 3773
(1997). Submitted to J. Phys. Soc. Jp
Spin Precession and Avalanches
In many magnetic materials, spin dynamics at short times are dominated by
precessional motion as damping is relatively small. In the limit of no damping
and no thermal noise, we show that for a large enough initial instability, an
avalanche can transition to an ergodic phase where the state is equivalent to
one at finite temperature, often above that for ferromagnetic ordering. This
dynamical nucleation phenomenon is analyzed theoretically. For small finite
damping the high temperature growth front becomes spread out over a large
region. The implications for real materials are discussed.Comment: 4 pages 2 figure
Hysteresis multicycles in nanomagnet arrays
We predict two new physical effects in arrays of single-domain nanomagnets by
performing simulations using a realistic model Hamiltonian and physical
parameters. First, we find hysteretic multicycles for such nanomagnets. The
simulation uses continuous spin dynamics through the Landau-Lifshitz-Gilbert
(LLG) equation. In some regions of parameter space, the probability of finding
a multicycle is as high as ~0.6. We find that systems with larger and more
anisotropic nanomagnets tend to display more multicycles. This result
demonstrates the importance of disorder and frustration for multicycle
behavior. We also show that there is a fundamental difference between the more
realistic vector LLG equation and scalar models of hysteresis, such as Ising
models. In the latter case, spin and external field inversion symmetry is
obeyed but in the former it is destroyed by the dynamics, with important
experimental implications.Comment: 7 pages, 2 figure
Ising Dynamics with Damping
We show for the Ising model that is possible construct a discrete time
stochastic model analogous to the Langevin equation that incorporates an
arbitrary amount of damping. It is shown to give the correct equilibrium
statistics and is then used to investigate nonequilibrium phenomena, in
particular, magnetic avalanches. The value of damping can greatly alter the
shape of hysteresis loops, and for small damping and high disorder, the
morphology of large avalanches can be drastically effected. Small damping also
alters the size distribution of avalanches at criticality.Comment: 8 pages, 8 figures, 2 colum
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