Magnetic anisotropy and low-energy spin waves in the Dzyaloshinskii-Moriya spiral magnet Ba_2 Cu Ge_2 O_7

New neutron diffraction and inelastic scattering experiments are used to investigate in detail the field dependence of the magnetic structure and low-energy spin wave spectrum of the Dzyaloshinskii-Moriya helimagnet Ba_2 Cu Ge_2 O_7. The results suggest that the previously proposed model for the magnetism of this compound (an ideal sinusoidal spin spiral, stabilized by isotropic exchange and Dzyaloshinskii-Moriya interactions) needs to be refined. Both new and previously published data can be quantitatively explained by taking into account the Kaplan-Shekhtman-Entin-Wohlman-Aharony (KSEA) term, a special magnetic anisotropy term that was predicted to always accompany Dzyaloshinskii-Moriya interactions in insulators.Comment: 30 pages, 10 figures, submitted to PR

Reversality of optical interactions in noncentrosymmetric media

The interaction of an electromagnetic wave with a noncentrosymmetric crystal is not necessarily time reversible, and the departure from reversality may be seen in nonlocal (wave-vector linear) phenomena. However, relativistic symmetry with respect to simultaneous time and space inversion is always preserved in optics

Structure of the exotic spin-flop states in BaCu2Si2O7

The unusual 2-stage spin flop transition in BaCu2Si2O7 is studied by single-crystal neutron diffraction. The magnetic structures of the various spin-flop phases are determined. The results appear to be inconsistent with the previously proposed theoretical explanation of the 2-stage transition.Comment: 6 pages 5 figure

Optical size control in growth of gallium nanoparticles

We report that a low level of optical excitation provides a substantial influence on the size distribution of gallium nanoparticles grown from the atomic beam on a cryogenic substrate, thus providing a new way of achieving tailored films of nanoparticles with given characteristics. The growth experiments, performed in situ in the vacuum chamber of a scanning electron microscope (SEM) equipped with an inverted effusion cell, revealed that the median diameter of the nanoparticles decreases with increasing irradiating optical power, with 0.1, 0.2 and 0.4 mW average power resulting in 70, 50 and 45 nm particles, respectively

Plasmonic absorption properties of bimetallic metamaterials

We demonstrate polarization controlled absorption in plasmonic bimetallic metamaterials. We fabricate and experimentally characterize Au/Ni ring resonator arrays, where by varying the wavelength and polarization of the incident wave, local electromagnetic fields and dissipation can be suppressed or enhanced in the Au and Ni areas of the rings

Phase-change memory functionality in gallium nanoparticles

We report that the structural phase of gallium nanoparticles can be switched by optical excitation and read via their cathodoluminescence (CL) when excited by a scanning electron beam. This opens a new paradigm in developing high-density phase change optical memory elements. A film of gallium nanoparticles was sputtered at the end face of an optical fiber, through which the reflectivity at 195 K was monitored by a 1.31 µm laser. By launching a single pulse from a 1.55 µm laser (17 mW, 1 µs) to the sample, a solid-to-liquid phase transition was observed as an immediate change of reflectivity from 10.0 to 10.5 %. CL spectra were measured immediately before and after the phase transition. The spectra show that gallium nanoparticles luminesce in the range of 400-650 nm, in which there at 520 nm is a 10 % difference of emission before and after the phase transition, due to a difference in optical properties. In future continuation of this first demonstration of electron beam read-out of the phase of nanoparticles, it is likely that the electron beam itself can change the phase of individual nanoparticles in the film, and that this phase furthermore can be read out at lower power by its cathode luminescence response with the same electron beam