Strangeness production in AA collisions at SIS18

Aluminium oxides doped with 1% ⁵⁷Fe were prepared by sol-gel method, and annealed for 3 hours at various temperatures between 550°C and 1100°C. Amorphous phases were obtained below 1000°C, and crystalline α–Al₂O₃ was formed at 1100°C. Although Al₂O₃ itself shows diamagnetism, the light doping of Fe ions into aluminium oxide induced a very weak ferromagnetism, but the ferromagnetism disappeared by longer annealing. M?ssbauer spectra were composed of paramagnetic Fe^2?+? and Fe^3?+? species for samples heated below 750°C, and of paramagnetic Fe^3?+? above 850°C, in addition to a magnetic sextet and relaxation peaks of Fe^3?+?. The magnetic and quadrupole interactions of the sextet and the relaxation peaks and the density functional calculations suggest that the lightly doped Fe^3?+? ions are substituted at Al sites in the Al₂O₃ lattice.     

M?ssbauer study of carbon coated iron magnetic nanoparticles produced by simultaneous reduction/pyrolysis

Magnetic iron nanoparticles immersed in a carbon matrix were produced by a combined process of controlled dispersion of Fe^3?+? ions in sucrose, thermal decomposition with simultaneous reduction of iron cores and the formation of the porous carbonaceous matrix. The materials were prepared with iron contents of 1, 4 and 8 in %wt in sucrose and heated at 400, 600 and 800°. The samples were analyzed by XRD, Mössbauer spectroscopy, magnetization measurements, TG, SEM and TEM. The materials prepared at 400° are composed essentially of Fe₃O₄ particles and carbon, while treatments at higher temperatures, e.g. 600 and 800° produced as main phases Fe⁰ and Fe₃C. The Mössbauer spectra of samples heated at 400° showed two sextets characteristic of a magnetite phase and other contributions compatible with Fe^3?+? and Fe^2?+? phases in a carbonaceous matrix. Samples treated at temperatures above 600° showed the presence of metallic iron with concentrations between 16?C43%. The samples heated at 800° produced higher amounts of Fe₃C (between 20% and 58%). SEM showed for the iron 8% sample treated at 600?C800°C particle sizes smaller than 50 nm. Due to the presence of Fe⁰ particles in the carbonaceous porous matrix the materials have great potential for application as magnetic adsorbents.     

High-temperature cation ordering in olivine: an in situ Mössbauer study of synthetic (Mg0.55Fe0.45)2 SiO4

High-temperature in situ Mössbauer spectroscopy measurements (300–950°C) were done on synthetic olivine of composition (Mg_0.55Fe_0.45)₂ SiO₄ (=Fa45) in order to study the distribution of Fe^2?+? over the M1 and M2 octahedral sites. The spectra are fit with two doublets, which are assigned to Fe^2?+? at the M1 (smaller splitting) and M2 sites. The Fe^2?+? site-occupancies at M1 and M2, obtained from the Mössbauer relative areas, suggest that Fe^2?+? has a slight preference for the M1 site at temperatures below ~500°C, with a tendency of disordering around this temperature. At higher temperatures, Fe^2?+? again prefers to occupy the M1 site, where it shows a considerable order at this site up to 750°C. At still higher temperatures, the spectra indicated partial reduction of the Fa-component into metallic iron and the resolution of the doublets was severely deteriorated.     

TL,OA and ESR of spessartine garnet

Thermoluminescence (TL), optical absorption (OA), electron spin resonance (ESR) and their relation to point defects in spessartine have been investigated. The TL glow curve presented four peaks at 150, 220, 260 and 335 °C. The 150 and 335 °C TL peaks growth curves presented a linear growth with radiation dose up to about 400 Gy, supralinearity above this dose, and saturation around 800–1000 Gy. The OA spectrum presented allowed spin transition bands due to Fe³⁺ and Mn²⁺ in dodecahedral environment. Absorption bands due to ultraviolet charge transfer of Fe³⁺ in octahedral and tetrahedral positions were also observed. Two ESR, a strong one around g?～?2 due to Fe³⁺ in octahedral position, and another weaker one at g?～?4 due to Fe³⁺ in tetrahedral position, have been detected. The effect of high temperature annealing (600–900 °C) before irradiation was also investigated.     

Characterization of Fe states in dilute 57 Mn implanted SnO 2 film

States of dilute Fe in SnO₂ have been monitored using ⁵⁷Fe emission Mössbauer spectroscopy following implantation of ⁵⁷Mn (T _1/2 = 85.4 s) in the temperature range from 143 K to 711 K. A sharp annealing stage is observed at ~330 K where the Fe^3?+?/Fe^2?+? ratio shows a marked increase. It is suggested that this annealing stage is due to the dissociation of Mn-V_O pairs during the lifetime of ⁵⁷Mn; the activation energy for this dissociation is estimated to be 0.9(1) eV. Fe^3?+? is found in a paramagnetic state showing spin-lattice relaxation rates consistent with an expected T ² dependence derived for a Raman process. In addition, a sharp lined doublet in the Mössbauer spectra is interpreted as due to recoil produced interstitial Fe.     

57Fe conversion electron Mössbauer spectrometric study of boron and carbon ion implanted irons

Amorphous layers produced at the surface of iron by B⁺ and C⁺ implantation (50 kV, 1×10¹⁸ ions cm⁻²) were analyzed by CEMS. The CEM spectrum of B⁺ implanted layer was composed of broad doublet and sextet. Spread hyperfine field distribution, P(H), indicates the formation of extremely disordered FeB layer. Annealing at 400°C brought about precipitation of FeB, which was converted to Fe₂B by annealing at 500°C. The P(H) for C⁺ implanted iron was resolved to 3 subpeaks with H values of 11.0, 18.0 and 22.5 T. The amorphous FeC phase was strongly correlated to crystalline Fe₅C₂ and Fe₂C, which precipitated at 300°C and were transformed into Fe₃C at 500°C. The amorphous layer disappeared by annealing at 600°C.     

Variety of available coordination sites for extra-framework iron in LTA and MFI zeolites

Variations in coordination states of extra-framework iron are studied in low iron content ferrisilicates (Si/⁵⁷Fe ≈ 200) during various in situ treatments. In Fe-LTA complete Fe³⁺ ? Fe^2?+? reversibility is observed. In Fe-MFI extra-framework iron can be stabilized in Fe^2?+? state in spite of ambient oxidizing conditions (N₂O, 620 K). Further, in Fe-MFI simultaneous stabilization of Fe^2?+? and Fe^3?+? may take place providing centres for redox catalytic processes.     

Thermal evolution of high dose iron implanted sintered alumina

Sintered plates of alumina have been implanted at room temperature with 110 keV⁵⁷Fe⁺ at a dose of 1.2×10¹⁷ ions.cm^?2. The analysis of the Conversion Electron Mössbauer Spectrum indicated that implantation introduces iron in alumina in three charge state: Fe²⁺ (two components), Fe⁴⁺ and Fe⁰ (metallic clusters). The evolution of the iron depth distribution during annealings in oxiding or in neutral atmosphere has been followed using the Rutherford backscattering spectroscopy. Up to 800°C the profile as well as the charge states of iron evolve very slowly. A drastic change occurs' for annealing temperature around 1000°C. The total amount of iron is distributed among α-Fe₂O₃ and α-(Fe_1?x Al _x )₂O₃ precipitates. Some scanning electron micrographs have allowed to locate these precipitates. For highest temperature anneals, up to 1600°C, only substitutional iron remain.     

Sol-gel synthesis and dilute magnetism of nano MgO powder doped with Fe

Mg oxides doped with 1 % ⁵⁷Fe were prepared by a sol-gel method, and annealed at various temperatures. Nano-size Mg oxides were characterized by Mössbauer spectrometry, magnetization and XRD measurements. The crystalline size of MgO increases with increase of annealing temperature. Samples annealed at 600 °C and 800 °C gave only doublet peaks of paramagnetic Fe³⁺ in Mössbauer spectra although Fe³⁺ doping into MgO induced a distorted structure and showed weak ferromagnetism. It is considered that the magnetic property is due to defect induced magnetism by doping Fe³⁺ into MgO. For a sample heated at 1000 °C, it is found from low temperature Mössbauer spectra that Fe³⁺ species are located at the core and shell of fine MgFe₂O₄ grains and diluted in MgO matrix.     

57Fe Mössbauer spectroscopy study of phlogopite megacrysts from an evolved carbonatitic kimberlite in the northeastern Oman Mountains

The Fe oxidation degree determined by ⁵⁷Fe Mössbauer spectroscopy and microprobe was used to characterize fresh and altered phlogopite megacrysts from an evolved carbonatitic kimberlite from northeastern Oman. The Quadrupole splitting (QS) varies between 2.19 and 2.48 mm/s (Fe^2?+?) in the fresh phlogopite samples and between 2.40 and 2.47 mm/s in the altered phlogopite samples. The quadrupole splitting of the Fe^3?+? doublets varies between 0.66 and 0.85 mm/s in the fresh samples. The altered phlogopite samples show three Fe^3?+? doublets; the first show a quadrupole splitting between 0.97 and 1.13, the second quadrupole splitting varies between 0.24 and 0.46 mm/s and the third varies between ??0.23 and ??0.35 mm/s. The phlogopite was observed to have an average Fe^3?+?/Fe_total of 35% to 37%, and corresponds to fresh phlogopite. The second one results from the alteration of the first type, and the Fe^3?+?/Fe_total ranges between 40% and 57%. Tetrahedral Fe^3?+? ions were confirmed in the altered phlogopite samples. Quantitative Fe site distributions can be obtained from room-temperature Mössbauer data if the different recoilless factors for octahedral Fe^2?+? and tetrahedral Fe^3?+? are considered. The observed isomer shifts are consistent with Mössbauer temperatures of 330 K, reported in the literature for tetrahedral and octahedral Fe^3?+? and Fe^2?+? in phlogopite. The results are compared to those obtained for natural and synthetic phlogopite from worldwide.     

Controlling magnetic properties of iron oxide nanoparticles using post-synthesis thermal treatment

Changes in morphological and magnetic properties of Fe₃O₄ nanoparticles before and after annealing are investigated in the present work. The nanoparticles are synthesized in a standard capacitively coupled plasma enhanced chemical vapour deposition system with two electrodes using ferrocene as the source compound. Post annealing, due to the sintering process, the particles fuse along with recrystallization. This results in increased size of the nanoparticles and the interparticle interaction, which play a major role in deciding the magnetic properties. X-ray diffraction patterns of the samples before and after annealing indicate a phase change from Fe₃O₄ to Fe₂O₃. Annealing at 200 ^°C causes the apparent saturation magnetization to increase from 6 emu?g^?1 to 15 emu?g^?1. When annealed at 500 ^°C, the magnetic properties of the nanoparticles resemble those of the bulk material. The evidence for the transition from a superparamagnetic state to a collective state is also observed when annealed at 500 ^°C. Variation of the magnetic relaxation data with annealing also reflects the change in the magnetic state brought about by the annealing. The correlation between annealing temperature and the magnetic properties can be used to obtain nanocrystallites of iron oxide with different sizes and magnetic properties.     

Kinetics of the nanocrystalline structure formation

The kinetics of the nanocrystalline structure formation in the Fe_73.5Cu₁Nb₃Si_22.5?xB_x (x=6. 7. 8. 9 at. %) was followed during the annealing runs interrupted between 300 and 700°C.⁵⁷Fe room temperature Mössbauer spectra were taken and complemented by the electrical resistivity and X-Ray diffraction measurements. It has been found that for the 50 K/min temperature increase the formation of the nanocrystalline phase begins above 450°C reaching a maximum around 500°C and is followed by the second stage of crystallization of the disordered intergranular remainder above ca 600°C accompanied by the changes in the occupation of the iron sites in the crystalline α?Fe?Si phase. Thus gained composition-temperature dependence seems to witness for the inhibiting influence of the substitution of B by Si on the crystallization process.     

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.     

Curie temperatures of CoPt ultrathin continuous films

The effects of layer thickness and thermal annealing on Curie temperature have been studied for CoPt ultrathin continuous layers in AlN/CoPt multilayer structures. It is found that there exists a critical thickness below which Curie temperature rapidly decreases due to the loss of spin-spin interactions in the vicinity of interface. After high temperature annealing, the in-plane lattice constant of CoPt film is increased and the exchange coupling parameter is decreased. Consequently, Curie temperatures decrease for some films with large thickness, compared with as-deposited state. Upon annealing at 600?^°C, CoPt undergoes ordering transformation, which also contributes to the degradation of the Curie temperature. However, when the CoPt film thickness is below 2?nm, the Curie temperature is increased after annealing. Especially for 1?nm thick film, the Curie temperature is strikingly increased from 173?^°C to 343?^°C after annealing at 600?^°C. This effect is attributed to the out-of-plane lattice deformation of CoPt thin layers in AlN/CoPt multilayer structures.     

Mössbauer and magnetic studies on nanocrystalline NiFe2O4 particles prepared by ethylene glycol route

NiFe₂O₄ nanoparticles have been synthesized by co-precipitation method at 145°C in N₂ atmosphere using ethylene glycol as solvent and capping agent. This gives the promising synthesis route for nanoparticles at low temperature. The as-synthesized NiFe₂O₄ is subsequently heated at 400°C, 500°C, 700°C and 800°C. Crystallite size increases with the heat treatment temperature. The heat treatment temperature has direct effect on the electron paramagnetic resonance and intrinsic magnetic properties. The room temperature Mössbauer spectrum of the 800°C heated sample shows the two sextets pattern indicating that the sample is ferrimagnetic and Fe^3?+? ions occupy both tetrahedral and octahedral sites of spinel structure.     

Einfluß des Kationenleerstellengehaltes auf die Lage des Curie-Punktes der Mn?Zn-Ferrite

A Curie point shift in Mn? Zn? Fe-ferrites after sintering or annealing at small partial oxygen pressures between 10^?1 and 10^?3 Torr at 1200°C was measured. The effect is explained with the increasing number of Zn-ions on B-sites and Fe^3?-ions on A-sites of the spinel lattice at high temperatures. Because of the small cation vacancy concentration at these partial oxygen pressures, the Zn-ions on B-sites cannot return on the A-sites during cooling and the Curie point is shifted to higher temperatures. The Curie point shift can be used to determine the stoichiometric state of Mn? Zn? Fe-ferrites, if the desaccommodation method and the determination of the active oxygen cannot be used.     

The origin of copiapite from chlorite pyritic schist (Wieściszowice, Lower Silesia, Poland) in the light of Mössbauer analysis

This work presents the results of the analysis of copiapite, formed from weathering and oxidation of pyrite in pyritic schist from Wie?ciszowice, Lower Silesia (Poland). The pure phase of copiapite was found in secondary minerals after pyrite and identified by optical microscopy, XRD and Mössbauer spectroscopy. In the analyzed copiapite major cations appear to be Fe^2?+? and Fe^3?+?. Some Fe^3?+? is substituted by other cations, mainly Al^3?+?. Al^3?+? probably comes from leaching of chlorite from which hydrated sulphates of iron, mainly szomolnokite, form followed by hydrated sulphates fibroferrite, which is replaced by copiapite.     

Study of SHI-induced ion beam mixing in Y3+: YIG employing X-ray diffraction and Mössbauer spectroscopy

The consequences of swift heavy ion (SHI) irradiation (Li^3?+?, 50 MeV, fluence =?5 × 10¹³ ions/cm²) on the structural and microscopic magnetic properties of Y^3?+?-substituted yttrium iron garnet (Y_3?+?x Fe_5???x O₁₂, x = 0.0, 0.2 and 0.4) have been studied at 300 K. It is found that an additional YFeO₃-phase observed along with bcc garnet phase, is completely removed for x = 0.2 composition while its percentage formation considerably reduces for x = 0.4 composition after irradiation. Similar effect has been observed for specimens sintered at 1,500°C. The SHI-induced ion beam mixing has been revealed through X-ray diffraction and Mössbauer spectroscopy.     

Mössbauer study of tektites

Room temperature ⁵⁷Fe Mössbauer spectroscopy has been used to investigate the structural and oxidation state of Fe in tektites from different strewn fields. Spectra have been analyzed in terms of two quadrupole splitting distributions corresponding to Fe^3?+? and Fe^2?+?. All tektites show similar distribution of quadrupole splitting. Each distribution has one peak. The Fe^2?+? sites show a narrow region of Mössbauer line shift (δ) and quadrupole splitting (ε), δ?= 1.02–1.10 mm/s and ε?= 0.85–1.00 mm/s relative to α-Fe. These values have been assigned to intermediate coordination between tetrahedral and octahedral. The Fe^3?+? sites show wider regions of hyperfine parameters: δ?= 0.25–0.45 mm/s and ε?= 0.65–0.90 mm/s. The Fe^3?+?/Fe^2?+? ratio was found to be 0.05–0.15.     

The system Na2CO3–MgCO3 at 3 GPa

It was suggested that Na–Mg carbonates might play a substantial role in mantle metasomatic processes through lowering melting temperatures of mantle peridotites. Taking into account that natrite, Na₂CO₃, eitelite, Na₂Mg(CO₃)₂, and magnesite, MgCO₃, have been recently reported from xenoliths of shallow mantle (110–115?km) origin, we performed experiments on phase relations in the system Na₂CO₃–MgCO₃ at 3?GPa and 800–1250°C. We found that the subsolidus assemblages comprise the stability fields of Na-carbonate?+?eitelite and eitelite?+?magnesite with the transition boundary at 50?mol% Na₂CO₃. The Na-carbonate–eitelite eutectic was established at 900°C and 69?mol% Na₂CO₃. Eitelite melts incongruently to magnesite and a liquid containing about 55?mol% Na₂CO₃ at 925?±?25 °C. At 1050 °C, the liquid, coexisting with Na-carbonate, contains 86–88?mol% Na₂CO₃. Melting point of Na₂CO₃ was established at 1175?±?25 °C. The Na₂CO₃ content in the liquid coexisting with magnesite decreases to 31?mol% as temperature increases to 1250°C. According to our data, the Na- and Mg-rich carbonate melt, which is more alkaline than eitelite, can be stable at the P–T conditions of the shallow lithospheric mantle with thermal gradient of 45?mW/m² corresponding to temperature of 900 °C at 3?GPa.