M. Rothermel

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 {approx_equal} 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.

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

Magnetic order in graphite: Experimental evidence, intrinsic and extrinsic difficulties

T_c \gtrsim 350

A comparison of the magnetic properties of proton- and iron-implanted graphite

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.

Defect-induced magnetism in homoepitaxial manganese-stabilized zirconia thin films

We discuss recently obtained data using different experimental methods including magnetoresistance measurements that indicate the existence of metal-free high-temperature magnetic order in graphite. Intrinsic as well as extrinsic difficulties to trigger magnetic order by irradiation of graphite are discussed in view of recently published theoretical work.

Comment on “Revealing common artifacts due to ferromagnetic inclusions in highly oriented pyrolytic graphite” by Sepioni M. et al.

Abstract.In this work we have investigated the changes of the magnetic properties of highly oriented pyrolytic graphite samples after irradiation either with ~3×1014 protons or 3.5×1013 ... 3.5×1014 iron ions with energies in the MeV range. Our results show that iron and proton irradiations can produce similar paramagnetic contributions depending on the implantation temperature. However, only protons induce a ferromagnetic effect.

3D ANALYSIS OF AN INDUCED ATHEROSCLEROTIC LESION IN A MURINE ARTERY BY PIXE STACKING

Ferromagnetic ordering is found for both undoped and Mn-doped zirconia (ZrO2 : Mn) thin films with 0 at% ≤ Mn ≤ 50 at% grown homoepitaxially on ZrO2 : Y2O3(0 0 1) substrates. Highly crystalline films show ferromagnetic saturation magnetization and coercive field at room temperature up to 1 emu cm−3 and 50 mT, respectively. The Curie temperature is in all ferromagnetic samples above 300 K. Comparing optimum films with different Mn content, cubic ZrO2 : Mn films with about 25 at% Mn show reproducibly the highest magnetization, in relation to monoclinic and tetragonal films. In contrast, less crystalline films grown heteroepitaxially on LaAlO3(0 0 1) or under non-ideal conditions show negligible magnetic effects.The fraction of paramagnetically active Mn atoms in a ZrO2 film with 27% Mn at 5 K is only about 1/5 of the incorporated Mn atoms, corresponding well to the share of 20% Mn4+ in XPS. Magnetic trace impurities in the 100 ppm range cannot account for the observed effects. Our results indicate that the observed defect-induced magnetic ordering in nominally non-magnetic zirconia thin films requires a certain balance of overall crystallinity, dislocation density and film mosaicity.

Limited angle STIM and PIXE tomography of single cells

aUniversität Leipzig, Institute for Experimental Physics II, Linnéstr. 5, 04103 Leipzig, Germany bCMAM and Instituto de Ciencia de Materiales “Nicolás Cabre ra”, Universidad Autónoma de Madrid, Cantoblanco, Madrid , Spain cInstituto de Fı́isica “Gleb Wataghin” DFA, Universidade Es tadual de Campinas-UNICAMP, Cidade Universitaria Zeferin o Vaz, Bairro, Barão Geraldo 13083-859, Brasil dStanford Synchrotron Radiation Lightsource, Stanford Uni versity, Menlo Park, CA 94025, USAThis 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.

Materials analysis and modification at LIPSION – Present state and future developments

Quantitative three dimensional analysis is possible, in principle, by PIXE tomography. But, the inherent problems in quantitation, restrictions on the sample geometry and preparation, and specimen damage due to high fluences make this method unsuitable for many biological samples. The specimen under investigation, a murine artery, was around a millimeter in diameter and the induced atherosclerotic lesion was spread few hundreds of micrometers across the length of the artery. Since no tomographic experiments were possible, we chose to do the 3D quantitative analysis by means of PIXE Stacking. Herein, thin serial sections of the specimen are prepared and measured by conventional ion beam techniques. The resultant two dimensional quantitative element maps are stacked and aligned to reconstruct a quantitative volume of the specimen. Although the reconstructed dimension has poorer spatial resolution as compared with the measured dimensions, new information can still be gained from it. The three dimensional element distribution of the atherosclerotic lesion shows calcification on the outer surface of the artery, which otherwise would not have been easily visible in the two dimensional analysis.