π\pi-Electron Ferromagnetism in Metal Free Carbon Probed by Soft X-Ray Dichroism

Elemental carbon represents a fundamental building block of matter and the possibility of ferromagnetic order in carbon attracted widespread attention. However, the origin of magnetic order in such a light element is only poorly understood and has puzzled researchers. We present a spectromicroscopy study at room temperature of proton irradiated metal free carbon using the elemental and chemical specificity of x-ray magnetic circular dichroism (XMCD). We demonstrate that the magnetic order in the investigated system originates only from the carbon $\pi$-electron system.Comment: 10 pages 3 color figure

Determining surface magnetization and local magnetic moments with atomic scale resolution

We propose a method to determine the direction of surface magnetization and local magnetic moments on the atomic scale. The method comprises high resolution scanning tunneling microscope experiments in conjunction with first principles simulations of the tunneling current. The potential of the method is demonstrated on a model system, antiferromagnetic Mn overlayers on W(110). We expect that it will ultimately allow to study the detailed changes of magnetic surface structures in the vicinity of dopants or impurities.Comment: Four pages (RevTeX) and five figures (EPS). For related papers see http://cmmp.phys.ucl.ac.uk/~wah

The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon $\pi$ states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top $\approx$10 nm of the irradiated sample where the actual magnetization reaches $\simeq 15$ emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite.Comment: 10 pages, 5 figures, 1 table, submitted to New Journal of Physic

Taxonomic revision and phylogeny of the Ophiocoma brevipes group (Echinodermata, Ophiuroidea) : with description of a new subgenus (Breviturma) and a new species

The taxonomy of the genus Ophiocoma was last revised by Devaney in 1970. Recent discoveries of new species and re-instatement of previously synonymized names suggest that we still do not fully understand the species limits in this genus. A recent biodiversity survey of the SW Indian Ocean shallow reefs strongly suggested an unrecognised species in the genus, closely related to O. brevipes/O. dentata. This study examined both the molecular phylogenetic relationships and the morphological characteristics of several species in the genus in order to characterise the unrecognised species. The focal species clusters with O. brevipes, O. dentata, O. doederleini within a monophyletic clade supported by molecular data for the first time. The name Breviturma subgen. nov. is proposed for this clade, previously known as brevipes group. Type material of nominal species that have been synonymized with O. dentata was examined and re-assessed. Ophiocoma marmorata proved not conspecific with O. dentata. A rarely used character, dorsal disc granule density, was tested and showed differences between the examined species at similar sizes. In combination with colour pattern, disc granule density, arm spine sequence and maximum disc size, the new species was delimited morphologically and described as Ophiocoma krohi sp. nov

Changing External Conditions and a Paradigm Shift in Regional Development Strategies?

Series: IIR-Discussion Paper