807 research outputs found
Comment on: "Revealing common artifacts due to ferromagnetic inclusions in highly oriented pyrolytic graphite", by M. Sepioni, R.R. Nair, I.-Ling Tsai, A.K. Geim and I.V. Grigorieva, EPL 97 (2012) 47001
This comment addresses several issues in the paper by Sepioni et al., where
it is stated that the ferromagnetism in pristine highly oriented pyrolytic
graphite (HOPG) reported by several groups in the previous years is most likely
due to impurity contamination. In this comment, clear arguments are given why
this statement is not justified. Furthermore, it is pointed out, that there are
already measurements using element-sensitive microscopic techniques, e.g. X-ray
Magnetic Circular Dichroism (XMCD) that directly proved the intrinsic origin of
the ferromagnetism in graphite, also in pristine HOPG.Comment: 1, 0 figures, 9 reference
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 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 10 nm of
the irradiated sample where the actual magnetization reaches 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
Atmospheric aerosol and Doppler lidar studies
Experimental and theoretical studies were performed of atmospheric aerosol backscatter and atmospheric dynamics with Doppler lidar as a primary tool. Activities include field and laboratory measurement and analysis efforts. The primary focus of activities related to understanding aerosol backscatter is the GLObal Backscatter Experiment (GLOBE) program. GLOBE is a multi-element effort designed toward developing a global aerosol model to describe tropospheric clean background backscatter conditions that Laser Atmospheric Wind Sounder (LAWS) is likely to encounter. Two survey missions were designed and flown in the NASA DC-8 in November 1989 and May to June 1990 over the remote Pacific Ocean, a region where backscatter values are low and where LAWS wind measurements could make a major contribution. The instrument complement consisted of pulsed and continuous-wave (CW) CO2 gas and solid state lidars measuring aerosol backscatter, optical particle counters measuring aerosol concentration, size distribution, and chemical composition, a filter/impactor system collecting aerosol samples for subsequent analysis, and integrating nephelometers measuring visible scattering coefficients. The GLOBE instrument package and survey missions were carefully planned to achieve complementary measurements under clean background backscatter conditions
Experimental Evidence for Two-Dimensional Magnetic Order in Proton Bombarded Graphite
We have prepared magnetic graphite samples bombarded by protons at low
temperatures and low fluences to attenuate the large thermal annealing produced
during irradiation. An overall optimization of sample handling allowed us to
find Curie temperatures K at the used fluences. The
magnetization versus temperature shows unequivocally a linear dependence, which
can be interpreted as due to excitations of spin waves in a two dimensional
Heisenberg model with a weak uniaxial anisotropy.Comment: 4 pages, 3 figure
07081 Abstracts Collection --- End-User Software Engineering
From 18.01.07 to 23.02.07, the Dagstuhl Seminar 07081 ``End-User Software Engineering\u27\u27 was held in the International Conference and Research Center (IBFI),
Schloss Dagstuhl.
During the seminar, several participants presented their current
research, and ongoing work and open problems were discussed. Abstracts of
the presentations given during the seminar as well as abstracts of
seminar results and ideas are put together in this paper. The first section
describes the seminar topics and goals in general.
Links to extended abstracts or full papers are provided, if available
Gravity compensation in complex plasmas by application of a temperature gradient
Micron sized particles are suspended or even lifted up in a gas by
thermophoresis. This allows the study of many processes occurring in strongly
coupled complex plasmas at the kinetic level in a relatively stress-free
environment. First results are presented. The technique is also of interest for
technological applications.Comment: 4 pages, 4 figures, final version to be published in Phys. Rev. Let
Proton-induced magnetic order in carbon: SQUID measurements
In this work we have studied systematically the changes in the magnetic
behavior of highly oriented pyrolytic graphite (HOPG) samples after proton
irradiation in the MeV energy range. Superconducting quantum interferometer
device (SQUID) results obtained from samples with thousands of localized spots
of micrometer size as well on samples irradiated with a broad beam confirm
previously reported results. Both, the para- and ferromagnetic contributions
depend strongly on the irradiation details. The results indicate that the
magnetic moment at saturation of spots of micrometer size is of the order of
emu.Comment: Invited contribution at ICACS2006 to be published in Nucl. Instr. and
Meth. B. 8 pages and 6 figure
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