136 research outputs found
Topologically Induced Optical Activity in Graphene-Based Meta-Structures
Non-reciprocity and asymmetric transmission in optical and plasmonic systems
is a key element for engineering the one-way propagation structures for light
manipulation. Here we investigate topological nanostructures covered with
graphene-based meta-surfaces, which consist of a periodic pattern of
sub-wavelength stripes of graphene winding around the (meta-) tube or
(meta-)torus. We establish the relation between the topological and plasmonic
properties in these structures, as justified by simple theoretical expressions.
Our results demonstrate how to use strong asymmetric and chiral plasmonic
responses to tailor the electrodynamic properties in topological
meta-structures. Cavity resonances formed by elliptical and hyperbolic plasmons
in meta-structures are sensitive to the one-way propagation regime in a finite
length (Fabry-Perot-like) meta-tube and display the giant mode splitting in a
(Mach-Zehnder-like) meta-torus.Comment: 20 pages, 5 figures + TOC figure, accepted by ACS Photonic
Radiation and Propagation of Waves in Magnetic Materials with Helicoidal Magnetic Structure
In this chapter, we are shortly reviewing some problems of electromagnetic and acoustic wave propagation and radiation in the magnets with helicoidal spin structure. We show the band structure of the coupled wave spectrum in the materials. The band gap width depends on the spiral angle (or, equivalently, on external magnetic field value). Interaction of spin and electromagnetic waves leads to opening the gap in spin-electromagnetic dispersion. This gap leads to opacity window in reflection spectrum of spiral magnet plate. The opacity window closes at phase transition into collinear ferromagnetic state and reaches a maximum at simple spiral state. At the frequencies near band gap boundaries, the rotation of polarization plane of propagating electromagnetic wave is observed. Account of interaction of spin and electromagnetic waves with acoustic subsystem leads to opening the gap in spin-acoustic spectrum. This gap leads to some features in electromagnetic reflectance spectrum and to rotation of acoustic wave polarization plane, i.e. to acoustic Faraday effect. We also show the possibility of acoustic and electromagnetic wave radiation by helicoidal magnets at phase transition into collinear ferromagnetic state. Some features of electromagnetic waves generation by spiral magnets placed in homogeneous magnetic field with harmonical time-dependence are also discussed
Magnetocaloric effect and magnetization in a Ni-Mn-Ga Heusler alloy in the vicinity of magnetostructural transition
The magnetic and thermodynamic properties of a Ni2.19Mn0.81Ga alloy with
coupled magnetic and structural (martensitic) phase transitions were studied
experimentally and theoretically. The magnetocaloric effect was measured by a
direct method in magnetic fields 0-26 kOe at temperatures close to the
magnetostructural transition temperature. For theoretical description of the
alloy properties near the magnetostructural transition a statistical model is
suggested, that takes into account the coexistence of martensite and austenite
domains in the vicinity of martensite transformation point.Comment: presented at ICM-2003, to appear in JMM
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