3D-Hydrogen analysis of ferromagnetic microstructures in proton irradiated graphite

Reichart, P.; Spemann, D.; Hauptner, A.; Bergmaier, A.; Hable, V.; Hertenberger, R.; Greubel, C.; Setzer, A.; Dollinger, G.; Jamieson, David N.; Butz, T.; Esquinazi, P.

doi:10.1016/j.nimb.2006.04.014

Cited by 20 publications

(14 citation statements)

References 24 publications

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“…The ratio between the inferred yield (based on cross-sections data [27]) and ours was found to be consistent with previous experimental evidence that 1 H and 2 H contaminations mostly come from the bulk of the targets rather than from their surface (∼ 0.3 at-ppm) [28]. However, since the nitrogen aquarium was found to reduce the target contamination, we can conclude that there is a target uptake of light contaminants from the residual gas.…”

Section: Discussionsupporting

confidence: 91%

Reduction of deuterium content in carbon targets for 12C + 12C reaction studies of astrophysical interest

et al. 2018

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Abstract. The12 C( 12 C, p) 23 Na and 12 C( 12 C, α) 20 Ne fusion reactions are among the most important in stellar evolution since they determine the destiny of massive (M 8-10 M ) stars. However, experimental low-energy investigations of such reactions are significantly hampered by ubiquitous natural hydrogen and deuterium contaminants in the carbon targets. The associated beam-induced background completely masks the reaction products of interest thus preventing cross-section measurements at the relevant energies of astrophysical interest, E cm < 2 MeV. In this work, we report about an investigation aimed at assessing possible deuterium reductions on both natural graphite and Highly Ordered Pyrolytic Graphite targets as a function of target temperature. Our results indicate that reductions up to about 80% can be attained on both targets in the temperature range investigated, T 200-1200 • C. A further reduction by a factor of 2.5 in absolute deuterium content is observed when the scattering chamber is surrounded by a dry nitrogen atmosphere so as to minimise light-particles uptake within the chamber rest gas (and thus on target) through air leaks. The results from this study will inform the choice of optimal experimental conditions and procedures for improved measurements of the 12 C + 12 C reactions cross-sections at the low energies of astrophysical interest.

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Section: Discussionsupporting

confidence: 91%

Reduction of deuterium content in carbon targets for 12C + 12C reaction studies of astrophysical interest

et al. 2018

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“…Three-dimensional hydrogen analysis done on irradiated micrometer size spots using 2.25 MeV H + ions on HOPG confirmed that the implanted H stays well located at the implanted sites, both laterally as well as in depth, in agreement with SRIM simulations and without having evidence of diffusion broadening along the implantation direction, i.e., the c axis. 25 On the other hand, clear evidence for lateral hydrogen diffusion due to thermal effects over large distances was also observed. 25 In Fig.…”

Section: B Monte Carlo Simulations: the Srim Programsmentioning

confidence: 95%

“…the first micron, shows a much larger hydrogen concentration than deeper inside a HOPG sample. 25,26 Furthermore, we note that a systematic and quantitative study of the relationship between the vacancy number in the graphite structure produced by mega-electron-volt ͑MeV͒ ions and the different magnetic contributions was not yet thoroughly published in the literature.…”

Section: Introductionmentioning

confidence: 99%

Magnetic properties of graphite irradiated with MeV ions

et al. 2010

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We have studied the change in the magnetic properties produced on highly oriented pyrolytic graphite samples by irradiation of H, C, and N ions in the mega-electron-volt energy range. The use of specially made sample holders for the magnetic measurements provided high reproducibility allowing us to obtain directly the irradiation effects without any corrections or subtractions. Our results show that three magnetic phenomena are triggered by the defects produced by the irradiation, namely, Curie-type paramagnetism, ferromagnetism and an anomalous paramagnetic state that appears as precursor of the magnetic ordered state. Using SRIM simulations to estimate the amount of vacancies produced by the irradiation, the Curie-type paramagnetic response indicates an effective Bohr magneton number per nominally produced vacancy p = 0.27Ϯ 0.02 B. Direct measurements of the surface sample temperature during irradiation and the decrease in the ͑as-received͒ paramagnetic as well as ferromagnetic contributions after irradiation indicate that self-heating is one of the causes for small yield of ferromagnetism. Taking into account the hydrogen distribution in the virgin samples, the obtained results indicate that the induced ferromagnetism appears when the average vacancy distance is ϳ2 nm in the near surface region.

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“…We note that large concentration of hydrogen is found in the first micrometer thick region at the surface of graphite samples [22]. Therefore we should take into account the possible influence of hydrogen in triggering localized as well as non-localized magnetic moments in the graphite layers [20,23].…”

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confidence: 99%

Experimental evidence for two-dimensional magnetic order in proton bombarded graphite

et al. 2007

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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 Tc 350 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. PACS numbers: 75.50.Pp,75.30.Ds Recent advances to develop nanographitic systems have led to a renewed interest on their electrical properties worldwide [1]. A single layer of graphite, the twodimensional (2D) graphene, appears to have quantum properties at room temperature[2] as well as rectifying electronic properties [3,4]. On the other hand, some of those properties were already observed in highly oriented pyrolytic graphite (HOPG) of low mosaicity, as the quantum Hall effect[5] and de Haas -van Halphen quantum oscillations even at room temperature [6]. The twodimensional properties of the graphene planes in graphite open up the possibility of using nanometer to micron size regions of graphite in new integrated devices with spintronic properties either through the use of ferromagnetic electrodes, e.g. spin-valves, and/or making graphite itself magnetic. In fact this has been a topic of study in the last years and reports exist showing magnetic hysteresis in blank graphite [7] but especially in proton bombarded graphite [8]. Severe limitations in the sensitivity and reproducibility of standard magnetometers added to annealing effects during bombardment, hindered the identification of a critical temperature T c as well as the characteristics and dimensionality of the ferromagnetic signals. The aim of this work is to show that specially prepared highly oriented pyrolytic graphite (HOPG) samples show ferromagnetic order with T c 350 K and the magnetization temperature dependence is in good agreement with a 2D anisotropic Heisenberg model (2DHM) and the presence of spin waves excitations [9,10,11].For the experiments we used four pieces of a HOPG sample grade ZYA, samples 1 to 4 (mass: 12.8, 12.5, 10.1, and 6 mg respectively) irradiated by a 2.25 MeV proton micro-beam (sample 4: 2.0 MeV, 0.8 mm broad beam) perpendicular to the graphite planes. With the micro-beam we produced several thousands of spots of ∼ 2 µm diameter each and separated by 5 µm (sample 1) or 10 µm (samples 2 and 3) distance, similarly to the procedure used in Ref. 12. Samples 1 and 2 were irradiated at 110 K whereas samples 3 and 4 at room temperature. Further irradiation parameters for sam-ple 1 (2,3,4) were: 51375 (25600,25600,6) spots, fluence: 0.124 (0.08,0.13,0.3) nC/µm 2 , total irradiated charge 46.9 (44.8,37.4,900) µC, and 1 nA proton current (100 nA for sample 4). The pieces we have irradiated showed an iron concentration (the only detected magnetic impurity) within the first 35 µm of ∼ (0.4±0.04) µg/g (< 0.1 ppm).Previous experiments [8] showed ferr...

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3D-Hydrogen analysis of ferromagnetic microstructures in proton irradiated graphite

Cited by 20 publications

References 24 publications

Reduction of deuterium content in carbon targets for 12C + 12C reaction studies of astrophysical interest

Reduction of deuterium content in carbon targets for 12C + 12C reaction studies of astrophysical interest

Magnetic properties of graphite irradiated with MeV ions

Experimental evidence for two-dimensional magnetic order in proton bombarded graphite

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