254,176 research outputs found
Modelling spin waves in noncollinear antiferromagnets: spin-flop states, spin spirals, skyrmions and antiskyrmions
Spin waves in antiferromagnetic materials have great potential for
next-generation magnonic technologies. However, their properties and their
dependence on the type of ground-state antiferromagnetic structure are still
open questions. Here, we investigate theoretically spin waves in one- and
two-dimensional model systems with a focus on noncollinear antiferromagnetic
textures such as spin spirals and skyrmions of opposite topological charges. We
address in particular the nonreciprocal spin excitations recently measured in
bulk antiferromagnet -- utilizing
inelastic neutron scattering experiments [Phys.\ Rev.\ Lett.\ \textbf{119},
047201 (2017)], where we help to characterize the nature of the detected
spin-wave modes. Furthermore, we discuss how the Dzyaloshinskii-Moriya
interaction can lift the degeneracy of the spin-wave modes in antiferromagnets,
resembling the electronic Rashba splitting. We consider the spin-wave
excitations in antiferromagnetic spin-spiral and skyrmion systems and discuss
the features of their inelastic scattering spectra. We demonstrate that
antiskyrmions can be obtained with an isotropic Dzyaloshinskii-Moriya
interaction in certain antiferromagnets.Comment: 26 pages, 9 figure
First-principles investigation of spin wave dispersions in surface-reconstructed Co thin films on W(110)
We computed spin wave dispersions of surface-reconstructed Co films on the
W(110) surface in the adiabatic approximation. The magnetic exchange
interactions are obtained via first-principles electronic structure
calculations using the Korringa-Kohn-Rostoker Green function method. We analyze
the strength and oscillatory behavior of the intralayer and interlayer magnetic
interactions and investigate the resulting spin wave dispersions as a function
of the thickness of Co films. In particular, we highlight and explain the
strong impact of hybridization of the electronic states at the Co-W interface
on the magnetic exchange interactions and on the spin wave dispersions. We
compare our results to recent measurements based on electron energy loss
spectroscopy [E. Michel, H. Ibach, and C.M. Schneider, Phys. Rev. B 92, 024407
(2015)]. Good overall agreement with experimental findings can be obtained by
considering the possible overestimation of the spin splitting, stemming from
the local spin density approximation, and adopting an appropriate correction.Comment: 14 pages, 14 figure
Characteristic functions on the boundary of a planar domain need not be traces of least gradient functions
Given a smooth bounded planar domain, we construct a compact set on the
boundary s.t. its characteristic function is not the trace of a least gradient
function. This generalize the construction of Spradlin and Tamasan [ST14] on
the disc
Episodic memory, the cotemporality problem, and common sense
Direct realists about episodic memory claim that a rememberer has direct contact with a past event. But how is it possible to be acquainted with an event that ceased to exist? That’s the so-called cotemporality problem. The standard solution, proposed by Sven Bernecker, is to distinguish between the occurrence of an event and the existence of an event: an event ceases to occur without ceasing to exist. That’s the eternalist solution for the cotemporality problem. Nevertheless, some philosophers of memory claim that the adoption of an eternalist metaphysics of time would be too high a metaphysical price to be paid to hold direct realist intuitions about memory. Although I agree with these critics, I will try to show two things. First, that this kind of “common sense argument” is far from decisive. Second, that Bernecker’s proposal remains the best solution to the cotemporality problem
- …