Magnetism at single isolated iron atoms implanted in graphite

M?ssbauer spectra obtained after implantation of 57Fe into highly oriented pyrolytic graphite (HOPG) show a combined magnetic and quadrupole interaction with a magnetic hyperfine field Bhf = 32.6 T at 14 K. Though magnetic effects in nominally diamagnetic HOPG have been reported recently, no experiment has previously shown the existence of magnetism at the atomic scale. The results suggest that magnetic ordering occurs by coupling of the Fe magnetic moment to structural and/or electronic magnetic defects induced by the probe atoms' implantation damage.     

Magnetism in electron-doped copper oxides

We report muon spin relaxation/rotation measurements on sintered powder samples of Nd_2−x Ce _x CuO_4−y and a large single crystal of Nd₂CuO_4−y . We find an electronic phase diagram which is quite similar to that of hole-doped superconductors such as La_2−x Sr _x CuO_4−y , although the doping of electrons into the system is less efficient in destroying the static moments on the copper spins. Static magnetic order in Nd₂CuO_4−y appears below about 250 K, and two spin reorientations are seen atT=75 K andT=35 K. Measurements of the magnetic field penetration depth have been unsuccessful due to the rare-earth paramagnetism of these materials.     

Nitrogen implanted in iron: AES and Pes study

AES and PES studies of nitrogen in iron implanted with molecular nitrogen ions having an energy of 120 keV and doses on the order of 10¹⁷ N-atoms/cm² were performed. Measuring nitrogen concentration depth profiles, a remarkable accumulation of nitrogen near surface was found besides the ordinary concentration maximum at the depth of mean projected range R_p of nitrogen ions. In addition to strong nitride bonding state a weakly bonded nitrogen was also observed. It manifested itself by time-dependent changes in spectra and by a distinct value of N 1s binding energy. The reasons for the concept of weakly bonded nitrogen, probably of molecular form, are discussed.     

One-dimensional iron oxides nanostructures

Iron oxides,including α-Fe2O3,γ-Fe2O3,Fe3O4,etc.are one of the most widely investigated materials for their fundamental properties and potential applications.One-dimensional(1-D) iron oxides nanostructures are the focus of recent research activities because of their wide applications in magnetic refrigeration,information storage,electronics,catalysts,Li-ion battery,pigment,gas sensors,etc.This review covers the recent progress in the synthesis,properties and applications of 1-D iron oxides nanostructures.Th...     

Morin transition in annealed iron implanted garnets

Y₃Fe₅O₁₂, Y₃Al₅O₁₂ and Gd₃Ga₅O₁₂ single crystal granets were implanted with 10¹⁷iron.cm⁻². Complementary techniques: CEMS, TEM and XRD at glancing angles have allowed to follow the behavior of implanted iron during thermal annealings. For Y₃Fe₅O₁₂ large α-Fe₂O₃ particles are formed after annealings and at 1200°C occurs a low temperature regime of the Morin transition at room temperature. For Y₃Al₅O₁₂, due to aluminium substitution in the precipitates, the Morin transition is only detected after an annealing at 1300°C whereas in Gd₃Ga₅O₁₂ no Morin transition is observed.     

YIG formation in annealed iron implanted YAG

YAG and YIG crystals implanted respectively with 100 keV⁵⁷Fe²⁺ ions (1 × 10¹⁷ ions.cm^?2) and 50 keV²⁷Al ions (1.1 × 10¹⁷ ions.cm^?2) have been studied by conversion electron Mössbauer spectroscopy (CEMS) directly after implantation and after annealings in air at temperatures up to 1100°C. In both as-implanted samples iron is found mainly in three states: Fe²⁺, Fe³⁺ and small metallic precipitates. Annealing behaviour is divided into two stages: (i) up to 400°C the iron has become completely oxidized and (ii) between 400 and 850°C the epitaxial regrowth of the implanted layer takes place. During this process a part of iron ions are incorporated into octahedral and tetrahedral sites, thus making a Y₃ (Al Fe)₅ O₁₂ compound. The remaining iron part precipitates in the form of Fe₂O₃ particles.     

CEMS study on aluminium implanted iron

Up to now a great deal of investigations in ion beam mixing of iron-aluminium layers are known. However, the easier way to produce such layers by direct implantation of aluminium ions in iron is less studied. In the present work aluminium implanted iron layers are studied. Iron samples were implanted with aluminium ions at 50, 100, and 200 keV, respectively, with doses between 5×10¹⁶ and 5×10¹⁷ cm⁻². Independent of energy, at doses up to 2×10¹⁷ cm⁻², besides alpha iron further magnetic fractions with a Fe₃Al-like structure are formed while at a dose of 5×10¹⁷ cm⁻² amorphous nonmagnetic components are formed.     

Annealing behaviour of iron implanted zirconia

A zirconia film was implanted at room temperature with 100 keV⁵⁷Fe⁺ to a fluence of 8×10¹⁶ ions/cm². The analysis of the Conversion Electron Mössbauer spectra shows that iron is distributed among different charge states: Fe⁰ (in a form of small and large metallic iron aggregates) Fe²⁺ and Fe⁴⁺. The evolution of the iron depth profile deduced from Rutherford backscattering measurements as well as the change in the charge states of iron as a function of annealing under argon atmosphere are presented.     

CEMS study of silicon implanted iron

Thin layers of iron-rich Fe-Si alloys were formed by silicon implantation into iron at room temperature with different energies (100, 200, and 300 keV) and ion doses (2 × 10¹⁷ to 1×10¹⁸ cm^–2). The produced layers were investigated by⁵⁷Fe conversion electron Mössbauer spectroscopy (CEMS) to identify the phases formed by the ion implantation. Auger electron spectroscopy (AES) was used to measure the concentration depth profiles of the implanted silicon. Depending on the implantation parameters different disordered Fe-Si structures were detected. At low doses only magnetic phases were formed while at high doses a non-magnetic phase with a hitherto unknown structure appeared. Annealing of the samples resulted first in the formation of a D0₃-like short-range order and a slow decrease of the non-magnetic phase, and subsequently in the migration of Si out of the investigated depth range.     

Local states of iron in iron implanted hematite Fe2O3

Powder samples of⁵⁷Fe₂O₃ and⁵⁶Fe₂O₃ were implanted with⁵⁶Fe and⁵⁷Fe ions, respectively. By the use of Conversion Electron Mössbauer Spectroscopy it was possible to observe the local states of implanted ions (⁵⁷Fe in⁵⁶Fe₂O₃) or the states of iron atoms from the target which were displaced during implantation due to the ballistic processes (⁵⁶Fe in⁵⁷Fe₂O₃). The implanted and displaced iron atoms appear in three different states: (i) in regular substitutional positions of Fe₂O₃, (ii) as magnetite Fe₃O₄-type structures and (iii) paramagnetic FeO_1?x state. The observed fractions of each state agree rather well with the calculated values obtained from the local iron atom enrichment at the surface as well as from the analysis of the equilibrium phase diagram for the binary Fe?O system. However, in⁵⁷Fe implanted samples some enhancement of the FeO_1?x fraction was found in comparison with the⁵⁶Fe implanted hematite.     

Hyperfine interactions of iron implanted into aluminium

Stable⁵⁷Fe implanted into Al at energies of 20 to 70 keV and doses of 10¹⁴ to 2·10¹⁷ ions/cm² was studied with conversion electron Mössbauer spectroscopy at room and liquid nitrogen temperatures. Spectra composed of a single line and a doublet were observed. Similarly as in the splat-quenched FeAl alloys iron monomers and iron associations, mostly dimers, are observed. The isomer shifts of both components differ considerably and do not change with iron concentration. The splitting of the doublet increases with iron concentration, the increase being reproduced by computer simulations of electric field gradients in lattices with a random distribution of charge defects. The observed probability of formation of iron associates is higher than in random systems, especially at high iron doses.     

Deep levels of iron implanted inn-type silicon

Results of an investigation of 19 organic dyes pumped by a 1.7 MW discharge-pumped XeCl excimer laser are reported. The dye-laser emission covered a wide wavelength range from 340 nm to 710 nm.P-terphenyl shows efficient laser action. The highest energy conversion efficiency exceeds 40% in visible region. In comparison with 250 kW nitrogen laser pumping, higher efficiencies are obtained for most of these dyes in the same dye-laser configuration.     

Photocatalytic efficiency of iron oxides: Degradation of 4-chlorophenol

The photocatalytic activity of ferrihydrite Fe₅O₇(OH)×4H₂O synthesized by homogeneous precipitation with urea and products obtained by calcinations of as-precipitated ferrihydrite at different temperatures (200–1000 °C) was studied. The microstructure and surface properties of raw precipitate and all heated samples were characterized by means of HRTEM, SEM, BET/BJH and RTG analyses. Kinetics of disappearance of 4-chlorophenol (4-CP) in aqueous solution was used as a test reaction. We have found that hematite Fe₂O₃ obtained at 1000 °C exhibited satisfied photocatalytic efficiency on the degradation of 4-CP.     

Origin of ferromagnetism in iron implanted rutile single crystals

⁵⁷Fe doped titanium oxide monocrystals, prepared by ion implantation at different temperatures and subsequent thermal treatment, were characterized by conversion electron Mössbauer spectrometry, synchrotron radiation x-ray diffraction and superconducting quantum interference device magnetometry. After implantation at room temperature Fe is present in divalent state. Upon annealing in high vacuum Fe^2?+? is reduced to metallic Fe for the most part. After implantation at 623 K most iron is in metallic state. During annealing on air Fe is gradually oxidized from Fe^2?+? to Fe^3?+?. Depending on preparation conditions and thermal treatment the role of different nanosized secondary phases is discussed in terms of their influence on the magnetic properties of Fe:TiO₂. α-Fe nanoparticles are found to be responsible for ferromagnetism observed in TiO₂.