Optically pumped laser generation at a long-wavelength edge of cholesteric photonic bandgap is detected in a dye-doped cholesteric cell with a hybrid alignment, where long axes of cholesteric molecules are parallel to one of the substrates and perpendicular to the opposite substrate in its close vicinity. The hybrid director alignment in the cell is confirmed by polarization optical microscopy observations in both reflection and transmission modes.

We describe a compact point laser source based on dye-doped cholesteric encapsulated in a flexible polymer film. Optically pumped emission spectra of the capsule are experimentally studied.

When the rare earth mononitrides (RENs) first burst onto the scientific scene in the middle of last century, there were feverish dreams that their strong magnetic moment would afford a wide range of applications. For decades research was frustrated by poor stoichiometry and the ready reaction of the materials in ambient conditions, and only recently have these impediments finally been overcome by advances in thin film fabrication with ultra-high vacuum based growth technology. Currently, the field of research into the RENs is growing rapidly, motivated by the materials demands of proposed electronic and spintronic devices. Both semiconducting and ferromagnetic properties have been established in some of the RENs which thus attract interest for the potential to exploit the spin of charge carriers in semiconductor technologies for both fundamental and applied science. In this review, we take stock of where progress has occurred within the last decade in both theoretical and experimental fields, and which has led to the point where a proof-of-concept spintronic device based on RENs has already been demonstrated. The article is organized into three major parts. First, we describe the epitaxial growth of REN thin films and their structural properties, with an emphasis on their prospective spintronic applications. Then, we conduct a critical review of the different advanced theoretical calculations utilized to determine both the electronic structure and the origins of the magnetism in these compounds. The rest of the review is devoted to the recent experimental results on optical, electrical and magnetic properties and their relation to current theoretical descriptions. These results are discussed particularly with regard to the controversy about the exact nature of the magnetic state and conduction processes in the RENs.

We report an interplay between magnetism and charge transport in the ferromagnetic semiconductor GdN, pointing to the formation of magnetic polarons centred on nitrogen vacancies. The scenario goes some way to resolving a long-standing disagreement between the measured and predicted Curie temperature in GdN. It further constitutes an extension of concepts that relate closely to the behaviour of ferromagnetic semiconductors generally, and EuO in particular.

The rare-earth nitrides are ferromagnetic semiconductors with promise for spintronic devices. Their most common dopants are nitrogen vacancies (VN), with a small enough energy of formation that they exist at of order 1% in epitaxial films. Here we report preliminary investigations of their effect on the magnetic states of two of them in the series, GdN and EuN. In the former we find an enhanced Curie temperature at very high VN concentration, and the Eu2+ ions associated with VN in the latter show strong exchange with their Eu3+ neighbours that might form the basis of a diluted magnetic semiconductor.

A summary of the magnetic properties of three Laves Phases compounds RFe2 (R = Pr, Nd, Yb) synthesized under high pressure is presented. Most of the results have been obtained by Mössbauer spectroscopy. Through the 57Fe resonance, the easy directions of magnetization between 4 and 300 K have been determined; the hyperfine field at Fe contains a large anisotropic contribution, only partly due to dipolar effects. From the Yb170 Mössbauer resonance measurements in YbFe2, the exchange field of the iron and the crystalline field, acting on Yb3+, have been derived.

Homoepitaxy of W(1 1 0) and Mo(1 1 0) is performed in a kinetically-limited regime to yield a nanotemplate in the form of a uniaxial array of hills and grooves aligned along the [0 0 1] direction. The topography and organization of the grooves were studied with RHEED and STM. The nanofacets, of type {2 1 0}, are tilted similar to 18 degrees away from (1 1 0). The lateral period could be varied from 4 to 12 nm by tuning the deposition temperature. Magnetic nanowires were formed in the grooves by deposition of Fe at 150 degrees C on such templates. Fe/W wires display an easy axis along [0 0 1] and a mean blocking temperature T-B approximate to 100 K. (C) 2007 Elsevier B.V. All rights reserved.

Homoepitaxy of W(110) and Mo(110) is performed in a kinetically-limited regime to yield a nanotemplate in the form of a uniaxial array of hills and grooves aligned along the [001] direction. The topography and organization of the grooves were studied with RHEED and STM. The nanofacets, of type {210}, are tilted ∼18° away from (110). The lateral period could be varied from 4 to 12nm by tuning the deposition temperature. Magnetic nanowires were formed in the grooves by deposition of Fe at 150°C on such templates. Fe/W wires display an easy axis along [001] and a mean blocking temperature TB≈100K.

We have revisited the epitaxial growth modes of Fe on W(110) and Mo(110), and propose an overview or our contribution to the field. We show that the Stranski–Krastanov growth mode, acknowledged for a long time in these systems, is in fact characterized by a bimodal distribution of islands for a growth temperature in the range ∼250–700 °C. We observe firstly compact islands whose shape is determined by Wulff–Kaischev’s theorem, and secondly thin and flat islands that display a preferred height, i.e. are independent of nominal thickness and deposition procedures (1.4 nm for Mo, and 5.5 nm for W on the average). We used this effect to fabricate self-organized arrays of nanometres-thick stripes by step decoration. Self-assembled nanoties are also obtained for nucleation of the flat islands on Mo at fairly high temperature, i.e. ∼800 °C. Finally, using interfacial layers and solid solutions we separate two effects on the preferred height, first that of the interfacial energy, and second that of the continuously varying lattice parameter of the growth surface.

The authors have self-organized versatile magnetic nanowires, i.e., with variable period and adjustable magnetic anisotropy energy (MAE). First, using the kinetic roughening of W(110), uniaxial templates of trenches were grown on commercial sapphire wafers. Unlike most templates used for self-organization, those have a variable period; 4–12nm are demonstrated here. Fe deposition then results in the formation of wires in the trenches. The magnitude of MAE could be engineered up or down by changing the capping layer or underlayer, in turn affecting the mean superparamagnetic temperature, raised to 175K so far.

A good astronomical site must fulfill several criteria including low atmospheric turbulence and low wind speeds. It is therefore important to have a detailed knowledge of the temperature and wind conditions of a location considered for future astronomical research. Antarctica has unique atmospheric conditions that have already been exploited at the South Pole station. Dome C, a site located on a local maximum of the Antarctic plateau, is likely to have even better conditions. In this paper we present the analysis of two decades of wind speed measurements taken at Dome C by an automated weather station (AWS). We also present temperature and wind speed profiles taken over four Antarctic summers using balloon-borne weather sondes. We will show that as well as having one of the lowest average wind speed ever recorded at an existing or potential observatory, Dome C also has an extremely stable upper atmosphere and a very low inversion layer.

Self-assembled bcc Fe(110) nanocrystals were grown by pulsed laser deposition on a Mo(110) buffer layer at high temperature. In the growth temperature range of 600--800 K, the resulting epitaxial Fe islands display a well-defined faceted shape elongated parallel to the in-plane Fe [001] lattice direction $(\ensuremath{\Vert}\mathrm{Mo}[001]).$ The lateral and vertical aspect ratios of the islands equal $L/w=1.9$ and $h/w=0.3,$ respectively, and remain nearly constant during the growth. The atomically flat facets were characterized by reflection high-energy electron diffraction and atomic force microscopy. They can be indexed as ${010}$ and ${110}$ bcc planes. The energy of an island was computed following the observed facet configuration, using tabulated data for surfaces and an interface energy ${E}_{\mathrm{int}}$ unknown a priori. The energy minimization calculation shows that the lateral and vertical aspect ratios correspond to the equilibrium shape of the crystal and also yields ${E}_{\mathrm{int}}=0.5\ifmmode\pm\else\textpm\fi{}0.2{\mathrm{J}/\mathrm{m}}^{2}.$ Decreasing the temperature below 600 K induces important changes in the density and in the shape of the islands. Wire shapes are obtained with islands aligned along the atomic steps of Mo(110), which is ascribed to kinetic limitations in the diffusion processes. Preliminary magnetic measurements show that the mean island shape controls the magnetic anisotropy of the system.

Rare-earth epitaxial thin films of Tb and Gd of the thicknesses between 2 nm and 16 nm were deposited by means of molecular beam epitaxy method. The roughness of the rare-earth films measured by scanning tunneling microscopy was fonnd to be in the range of 1-4.5 nm. The influence of the roughness on the dipolar anisotropy and magnetocrystalline surface anisotropy was estimated. The magnetic measurements have shown that the Gd layers deposited on the Y buffer layers had an easy plane anisotropy. However, for 2 nm thick Gd layer deposited on W buffer layer the perpendicular anisotropy was observed. According to the roughness analysis the possible sources of the perpendicular anisotropy in this sample is mainly the magnetoelastic anisotropy, but the presence of the magnetocrystalline surface anisotropy also cannot be neglected.

Cr/Tb/Cr thin films have been obtained by pulsed laser deposition (PLD) on sapphire (112̅0) substrates. The crystal structure of the films was characterised in-situ by means of reflection high energy electron diffraction (RHEED) and Auger spectroscopy (AS) and ex-situ by X-ray grazing incidence diffraction (GID) and scanning tunnelling microscopy (STM). The deposition of chromium on the Tb(0001) layers at 300 °C was found to lead to the formation of three Cr(110) crystalline domains. Chromium deposited on Tb(0001) initially (first 50 Å) at room temperature and then at 300 °C grew epitaxially in the [111] direction and formed two Cr(111) crystalline domains shifted by 30°. Due to the lower density of the atoms in Cr(111) plane, compared to the Cr(110) and Cr(001) ones, this orientation is interesting for magnetic studies.