Resonant optical effects in composite Co/opal-based magnetoplasmonic structures.

Plasmonic structures are extremely attractive for the light flow manipulation. In turn, the spectrum of the plasmon excitations can be controlled by external magnetic field, thus giving rise to magnetoplasmonics. However, in the case of traditional magnetoplasmonic structures, the enhancement of magneto-optical (MO) effects is often accompanied by the transmission damp, which constricts the area of their applications. This paper examines resonant optical effects in composite structures based on artificial opal films covered by a thin cobalt layer, which forms a 2D hexagonal lattice of nanoholes in the metal film. Such periodic structure exhibits surface plasmon polariton-assisted extraordinary transmission along with the increase of odd in magnetization intensity magnetooptical effect in the Voigt geometry. Local field enhancement accompanying the surface plasmon polaritons excitation in composite Co/opal structure provides a distinct enhancement of the magnetization-induced second harmonic generation (SHG) and relevant MO effects at the SHG wavelength that appear as Fano-type resonances. High transmission along with resonantly-high MO effects make Co/opal films promising in plasmonic applications.

Manipulation of the Dzyaloshinskii-Moriya Interaction in Co/Pt Multilayers with Strain.

Interfacial Dzyaloshinskii-Moriya interaction (DMI) is experimentally investigated in Pt/Co/Pt multilayer films under strain. A strong variation (from 0.1 to 0.8 mJ/m^{2}) of the DMI constant is demonstrated at ±0.1% in-plane uniaxial deformation of the films. The anisotropic strain induces strong DMI anisotropy. The DMI constant perpendicular to the strain direction changes sign, while the constant along the strain direction does not. Estimates show that the DMI can be controlled with an electric field in hybrid ferroelectric-ferromagnetic systems. So, the observed effect opens the way to control the DMI and eventually skyrmions with a voltage via a strain-mediated magnetoelectric coupling.

Magnetic Force Microscopy of Nanostructured Co/Pt Multilayer Films with Perpendicular Magnetization.

We present the results of magnetic force microscopy investigations of domain structures in multilayer [Co (0.5 nm)/Pt (1 nm)]5 thin film structures (denoted hereafter as Co/Pt) modified by additional Co capping layers and by ion irradiation. It is demonstrated that a Co capping layer essentially changes the domain structure and decreases the threshold of magnetization reversal, due to the formation of noncollinear magnetization in Co/Pt. It is shown that local irradiation with a focused He⁺ ion beam enables the formation of regions with decreased easy-axis anisotropy (magnetic bubbles) that have the inverse magnetization direction in the demagnetized state of Co/Pt. The experimental results demonstrate that the magnetic bubbles can be switched using a probe of a magnetic force microscope. The possible application of these effects for the development of magnetic logic and data storage systems is discussed.

Optical and magneto-optical resonances in nanocorrugated ferromagnetic films.

We report here on optical and magneto-optical spectra investigations of nanostructured Co and Ni films deposited on top of polymethyl methacrylate (PMMA) colloidal crystal. Resonant peculiarities have been observed in both spectra; their positions are scaled with the PMMA sphere diameter and depend on incident angle. Asymmetry of the resonance lineshapes as well as change of the direction of magneto-optical rotation has been observed. Both the surface plasmon resonance and the interference between reflections from the colloidal crystal and from the nanostructured film should be considered to explain the obtained results.

Velocity distributions of granular gases with drag and with long-range interactions.

We study velocity statistics of electrostatically driven granular gases. For two different experiments, (i) nonmagnetic particles in a viscous fluid and (ii) magnetic particles in air, the velocity distribution is non-Maxwellian, and its high-energy tail is exponential, P(upsilon) approximately exp(-/upsilon/). This behavior is consistent with the kinetic theory of driven dissipative particles. For particles immersed in a fluid, viscous damping is responsible for the exponential tail, while for magnetic particles, long-range interactions cause the exponential tail. We conclude that velocity statistics of dissipative gases are sensitive to the fluid environment and to the form of the particle interaction.

Far-from-equilibrium Ostwald ripening in electrostatically driven granular powders.

We report an experimental study of cluster size distributions in electrostatically driven granular submonolayers. The cluster size distribution in this far-from-equilibrium process exhibits dynamic scaling behavior characteristic of the (nearly equilibrium) Ostwald ripening, controlled by the attachment and detachment of the "gas" particles. The scaled size distribution, however, is different from the classical Wagner distribution obtained in the limit of a vanishingly small area fraction of the clusters. A much better agreement is found with the theory of Phys. Rev. E 65, 046117 (2002)] which accounts for the cluster merger.

Self-assembly and vortices formed by microparticles in weak electrolytes.

We carried out experimental studies of the self-assembly of metallic micron-size particles in poorly conducting liquid subject to a constant electric field. Depending on the experimental conditions, the particles self-assemble into long chains directed along the electric field lines and form vortices and other structures. The vortices perform Brownian-type random motion due to self-induced chaotic hydrodynamic flows. We measured the diffusivity constant of the vortices and the conductivity and mechanical stiffness of the chains.

Theory of pattern formation of metallic microparticles in poorly conducting liquids.

We develop a continuum theory of self-assembly and pattern formation in metallic microparticles immersed in a poorly conducting liquid in a dc electric field. The theory is formulated in terms of conservation laws for the densities of immobile particles (precipitate) and bouncing particles (gas) coupled to the Navier-Stokes equation for the liquid. This theory successfully reproduced the correct topology of the phase diagram and primary patterns observed in the experiment [Phys. Rev. Lett. 90, 114301 (2003)]]: static crystals, honeycombs, dynamic pulsating rings, and rotating multipetal vortices.

Dynamic self-assembly and patterns in electrostatically driven granular media.

We show that granular media, consisting of metallic microparticles immersed in a poorly conducting liquid in a strong dc electric field, self-assemble into a rich variety of novel phases. These phases include static precipitates: honeycombs and Wigner crystals; and novel dynamic condensates: toroidal vortices and pulsating rings. The observed structures are explained by the interplay between charged granular gas and electrohydrodynamic convective flows in the liquid.

Coarsening of granular clusters: Two types of scaling behaviors.

We report on an experimental study of small cluster dynamics during the coarsening process in driven granular submonolayers of 120-microm bronze particles. The techniques of electrostatic and vertical mechanical vibration were employed to excite the granular gas. We measure the scaling exponent for the evaporation of small clusters during coarsening. It was found that the surface area of small clusters S vs time t behaves as S to (t(0)-t)(2/3) for lower frequencies and S to (t(0)-t) for higher frequencies. We argue that the change in the scaling exponent is related to the transition from three-dimensional (3D) to 2D character of motion in the granular gas.