1,154 research outputs found
Spin canting induced large nonreciprocal Goos-Hänchen shifts
Recent studies on surface reflection illustrate how light beams can be laterally shifted from the position predicted by geometrical optics, the so called Goos-Hänchen effect. In antiferromagnets this shifts can be controlled with an external magnetic field. We show that a configuration in which spins cant in response to applied magnetic fields enhance possibilities of field controlled shifts. Moreover, we show that nonreciprocal displacements are possible, for both oblique and normal incidence, due to inherent nonreciprocity of the polariton phase with respect to the propagation direction. In the absence of an external field, reciprocal displacements occur
Disorder regimes and equivalence of disorder types in artificial spin ice
The field-induced dynamics of artificial spin ice are determined in part by
interactions between magnetic islands, and the switching characteristics of
each island. Disorder in either of these affects the response to applied
fields. Numerical simulations are used to show that disorder effects are
determined primarily by the strength of disorder relative to inter-island
interactions, rather than by the type of disorder. Weak and strong disorder
regimes exist and can be defined in a quantitative way.Comment: The following article has been submitted to J. Appl. Phys. After it
is published, it will be found at http://link.aip.org/link/?ja
Diversity enabling equilibration: disorder and the ground state in artificial spin ice
We report a novel approach to the question of whether and how the ground
state can be achieved in square artificial spin ices where frustration is
incomplete. We identify two types of disorder: quenched disorder in the island
response to fields and disorder in the sequence of driving fields. Numerical
simulations show that quenched disorder can lead to final states with lower
energy, and disorder in the driving fields always lowers the final energy
attained by the system. We use a network picture to understand these two
effects: disorder in island responses creates new dynamical pathways, and
disorder in driving fields allows more pathways to be followed.Comment: 5 pages, 5 figure
Vertex dynamics in finite two dimensional square spin ices
Local magnetic ordering in artificial spin ices is discussed from the point
of view of how geometrical frustration controls dynamics and the approach to
steady state. We discuss the possibility of using a particle picture based on
vertex configurations to interpret time evolution of magnetic configurations.
Analysis of possible vertex processes allows us to anticipate different
behaviors for open and closed edges and the existence of different field
regimes. Numerical simulations confirm these results and also demonstrate the
importance of correlations and long range interactions in understanding
particle population evolution. We also show that a mean field model of vertex
dynamics gives important insights into finite size effects.Comment: 4 pages, 4 figures; v2: minor changes to text and figures. Accepted
to Phys. Rev. Let
Effect of weak disorder on the ground state of uniaxial dipolar spin systems in the upper critical dimension
Extensive Monte Carlo simulations are used to investigate the stability of
the ferromagnetic ground state in three-dimensional systems of Ising dipoles
with added quenched disorder. These systems model the collective ferromagnetic
order observed in various systems with dipolar long-range interactions. The
uniaxial dipolar spins are arranged on a face-centred cubic lattice with
periodic boundary conditions. Finite-size scaling relations for the pure
dipolar ferromagnetic system are derived by a renormalisation group
calculation. These functions include logarithmic corrections to the expected
mean field behaviour since the system is in its upper critical dimension.
Scaled data confirm the validity of the finite-size scaling description and
results are compared with subsequent analysis of weakly disordered systems. A
disorder-temperature phase diagram displays the preservation of the
ferromagnetic ground state with the addition of small amounts of disorder,
suggesting the irrelevance of weak disorder in these systems.Comment: 6 pages, 4 figures; proceedings of the 3rd NEXT-Sigma-Phi Conference,
Kolymbari, Greece, August 200
Parallel axis theorem for free-space electron wavefunctions
We consider the orbital angular momentum of a free electron vortex moving in
a uniform magnetic field. We identify three contributions to this angular
momentum: the canonical orbital angular momentum associated with the vortex,
the angular momentum of the cyclotron orbit of the wavefunction, and a
diamagnetic angular momentum. The cyclotron and diamagnetic angular momenta are
found to be separable according to the parallel axis theorem. This means that
rotations can occur with respect to two or more axes simultaneously, which can
be observed with superpositions of vortex states
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