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We have developed an empirical model to determine Mossbauer isomer-shift of dilute Fe2+ impurities in ionic and covalent binary compounds, where at least one of the host belongs to the metalloids or non-metals category of the periodic system. The proposed approach employs the use of nearest neighbour distances and differences in host atoms Pauling electronegativity. The two-parameter model predicts the room temperature isomer-shift of 22 compounds with room temperature isomer shifts ranging from −0.93 mm/s to +0.95 mm/s with a standard deviation of 0.09 mm/s and is valid for difference in host atoms Pauling electronegativity of ΔχP

The properties and performance of TiN thin films are closely related to the concentration and mobility of lattice defects in the thin film structures of TiN. This makes a local atomic scale study of TiN thin films an ever-growing demand. Emission 57Fe Mössbauer spectroscopy (eMS) is a powerful tool in this regard, which we apply here to study an ultrathin TiN film epitaxially grown on MgO (100). With the help of theoretical calculations, our results show that most implanted Fe ions adopt a 2+ valence state and locate at the Ti sublattice in the bulk-like single crystalline grains, with the rest Fe residing at the grain boundaries as interstitials. A small percentage of nitrogen point defects (vacancy VN and interstitial NI) are observed in the bulk-like crystalline grains. A temperature-dependent, interstitial NI mediated site-exchange between NI and VN inside the crystal grain are deduced via a N2 dimmer like diffusion of NI through the crystal grains in the temperature range of 540 - 620 K. This is interesting in the perspective of exploring the catalytic property of TiN nanostructures. The titanium vacancy (VTi) is only detected at the grain boundaries. Annealing up to 813 K, both the VN and NI are annihilated in the crystalline grains and the VTi is fully recovered with healing of the grain boundaries. However, no evidence of ferromagnetism due to dilute implantation of 57Mn/57Fe and or structural defects in the film is obtained. This suggests that the so far reported dilute magnetism and defect-induced ferromagnetism in TiN nanostructures requires a further systematic investigation.

An extension of the online implantation chamber used for emission Mossbauer Spectroscopy (eMS) at ISOLDE/CERN that allows for quick removal of samples for offline low temperature studies is briefly described. We demonstrate how online eMS data obtained during implantation at temperatures between 300 K and 650 K of short-lived parent isotopes combined with rapid cooling and offline eMS measurements during the decay of the parent isotope can give detailed information on the binding properties of the Mossbauer probe in the lattice. This approach has been applied to study the properties of Sn impurities in ZnO following implantation of In-119 (T-1/2 = 2.4 min). Sn in the 4+ and 2+ charge states is observed. Above T > 600 K, Sn2+ is observed and is ascribed to Sn on regular Zn sites, while Sn2+ detected at T < 600 K is due to Sn in local amorphous regions. A new annealing stage is reported at T approximate to 550 K, characterized by changes in the Sn4+ emission profile, and is attributed to the annihilation of close Frenkel pairs. We acknowledge the support of the ISOLDE collaboration and technical teams. Fruitful discussion with Professor D. C. Lupascu University of Duisburg-Essen is acknowledged. I.U. acknowledges the support of the Ministry of Economy and Competitiveness (MINECO/FEDER) under Project No. RTI2018-094683-B-C55 and Basque Government Grant No. IT-1005-16. K.B.R., H.M., and D.N. acknowledge the support of Department of Science and Innovation (South Africa). B.Q., S.., and H.P.G. acknowledge support from the University of Iceland Research Fund. J. G. Martins Correia is acknowledged for technical assistance during the beam time. The Federal Ministry of Education and Research (BMBF) through Grant Nos. 05K16PGA, 05K16SI1, and 05K19SI1 "eMMA" is acknowledged. The European Commission through the Horizon 2020 programme (Grant Nos. 654002 and ENSAR 2) is acknowledged.

The atomic, magnetic and nano-structure of hydro­thermally synthesized non-stoichiometric spinel iron oxide nanoparticles are examined in detail using a wide range of advanced structural characterization methods. The present study constitutes the first use of the recently developed magnetic pair-distribution-function analysis method to model the local magnetic structure in nanoparticles., Spinel iron oxide nanoparticles of different mean sizes in the range 10–25 nm have been prepared by surfactant-free up-scalable near- and super-critical hydro­thermal synthesis pathways and characterized using a wide range of advanced structural characterization methods to provide a highly detailed structural description. The atomic structure is examined by combined Rietveld analysis of synchrotron powder X-ray diffraction (PXRD) data and time-of-flight neutron powder-diffraction (NPD) data. The local atomic ordering is further analysed by pair distribution function (PDF) analysis of both X-ray and neutron total-scattering data. It is observed that a non-stoichiometric structural model based on a tetragonal γ-Fe2O3 phase with vacancy ordering in the structure (space group P43212) yields the best fit to the PXRD and total-scattering data. Detailed peak-profile analysis reveals a shorter coherence length for the superstructure, which may be attributed to the vacancy-ordered domains being smaller than the size of the crystallites and/or the presence of anti-phase boundaries, faulting or other disorder effects. The intermediate stoichiometry between that of γ-Fe2O3 and Fe3O4 is confirmed by refinement of the Fe/O stoichiometry in the scattering data and quantitative analysis of Mössbauer spectra. The structural characterization is complemented by nano/micro-structural analysis using transmission electron microscopy (TEM), elemental mapping using scanning TEM, energy-dispersive X-ray spectroscopy and the measurement of macroscopic magnetic properties using vibrating sample magnetometry. Notably, no evidence is found of a Fe3O4/γ-Fe2O3 core-shell nanostructure being present, which had previously been suggested for non-stoichiometric spinel iron oxide nanoparticles. Finally, the study is concluded using the magnetic PDF (mPDF) method to model the neutron total-scattering data and determine the local magnetic ordering and magnetic domain sizes in the iron oxide nanoparticles. The mPDF data analysis reveals ferrimagnetic collinear ordering of the spins in the structure and the magnetic domain sizes to be ∼60–70% of the total nanoparticle sizes. The present study is the first in which mPDF analysis has been applied to magnetic nanoparticles, establishing a successful precedent for future studies of magnetic nanoparticles using this technique.

Understanding the mechanisms of magnetoelectric (ME) coupling within multiferroic structures is paramount from a fundamental as well as an applied point of view. We report here that the magnetoelectric properties, as well as the magnetization, of BaTiO$_3$-BiFeO$_3$ superlattices can be tuned by varying the BiFeO$_3$ layer thickness. The magnetoelectric voltage coefficient ($\alpha_{ME}$) reaches its maximum of 60.2 Vcm$^{-1}$Oe$^{-1}$ at 300 K, one of the highest values reported so far, for a sample with a BiFeO$_3$ thickness of 5 nm and a BaTiO$_3$ thickness of 10 nm. To gain deeper insight into the increased magnetoelectric coupling, and both the local and macroscopic magnetic properties, samples with varying BiFeO$_3$ thicknesses have been investigated. Correlations were established between the hyperfine field (HFF), the magnetoelectric voltage coefficient and the magnetization. The possible mechanisms responsible for the strong magnetoelectric coupling are discussed.

The deposition of volcanic ash from explosive eruptions to the surface ocean is a source of iron (Fe) for marine phytoplankton. However, the factors that determine the soluble and thus, potentially bioavailable, fraction of Fe in ash from magma source to ocean sink remain poorly understood. We investigate for the first time the release of both Fe(II) and Fe(III) from six natural ash samples in pH 1 H2SO4 representative of exposure to aqueous low pH conditions during airborne transport. Mossbauer spectroscopy analysis of the ash suggests that the overall (168 h) trends in Fetot and Fe(II)/Fetot release by individual samples are governed by dissolution of Fe-bearing aluminosilicates or oxides of the ash bulk. In contrast, the initial (

Microscopic understanding the metal-to-insulator transition (MIT) in strongly correlated materials is critical to the design and control of modern “beyond silicon” Mott nanodevices. In this work, the local MIT behaviors in single crystalline V2O3 thin films were probed on an atomic scale by online 57Fe emission Mossbauer spectroscopy (eMS) following dilute (

Publisher's version (útgefin grein), The current work presents a contemporary design of an advanced emission Mössbauer Spectrometer: eMIL equipped with a parallel-plate avalanche detector, which has been devised and built for the Mössbauer collaboration at ISOLDE/CERN. The setup is based on emission geometry, combined with on-line/off-line isotope implantation and provides numerous advantages over conversion electron, common emission (where isotope is deposited chemically on a sample) or transmission Mössbauer spectroscopy. eMIL is designed to measure hyperfine interactions in solids under various exposures. The implemented design overcomes limitations and improves performance and handling. In the current revision, the chamber is supplied with an UV extension — allowing to perform studies of photo-catalytic materials under external light exposure. A specifically designed motorized lid-samples-holder is fully automatized, and makes it possible to study up to 4 samples loaded in a magazine within a temperature range from RT up to 1100 K and to perform angular dependent measurements in high vacuum. This work additionally briefly describes data acquisition with additional electronic blocks, vacuum and data-acquisition system construction., Authors are indebted to Sergii Skoblikov for his significant assistance during the spectrometer assembling. This work is supported by the German Federal Ministry of Education and Research (BMBF) projects 05K16SI1 and 05K19SI1 . Fredericus M. A. Linderhof thanks the internal IGA grant of Palacký University ( IGA_PrF_2020 _011 ).

The change in the Curie temperature of single crystalline garnet Y3Fe5O12 (YIG) sample due to lattice damage induced by ion implantation has been investigated in 57Fe emission Mossbauer Spectroscopy (eMS) following implantation of 57Mn (T½ = 1.5 min). The Mossbauer spectra analysis reveal high spin Fe3+ ions substituted on both the octahedral and the tetrahedral sites. Measurements in the temperature range 298 K–798 K show that average values of the magnetic hyperfine field are decreased by the implantation-induced damage on the local lattice structure of the YIG. The Curie temperature, however, is determined to be 651 ± 5 K, considerably higher than the value of bulk YIG (559 K). This is most likely due to lattice damage-induced changes on the spin configurations of YIG through a FeA-O-FeD distortion scheme.

The compression mechanism of Fe1.087Te was studied by high-pressure X-ray diffraction at ambient temperature. Fe1.087Te retains tetragonal symmetry up to the highest measured pressure of 25.67 GPa and the structural parameters obtained by high-pressure X-ray diffraction were used as input parameters for electronic structure calculation at the DFT level. The electronic structure calculations show that the chemical bonding between Te atoms across the van der Waals gap is enhanced at elevated pressures and the Fermi surface undergoes at topological change at ≈4 GPa reflecting a change from 2- to 3-dimensional character of the electronic structure. Mössbauer spectra of Fe1.087Te recorded at elevated pressures and ambient temperature showed no indication of a pressure-induced change of the spin-state and the obtained isomer shifts and quadrupole splittings are consistent with Fe2+ ion with S = 1.

$\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ and related alloys are model systems of the coupling between structure and magnetism in solids. Since different electronic states (with different volumes and magnetic ordering states) are closely spaced in energy, small perturbations can alter which one is the actual ground state. Here, we demonstrate that the ferromagnetic state of $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ nanoparticles is associated with a tetragonal distortion of the fcc structure. Combining a wide range of complementary experimental techniques, including low-temperature M\"ossbauer spectroscopy, advanced transmission electron microscopy, and synchrotron radiation techniques, we unambiguously identify the tetragonally distorted ferromagnetic ground state, with lattice parameters $a=3.76(2)\phantom{\rule{4pt}{0ex}}\AA{}$ and $c=3.50(2)\phantom{\rule{4pt}{0ex}}\AA{}$, and a magnetic moment of 2.45(5) ${\ensuremath{\mu}}_{B}$ per Fe atom. Our findings indicate that the ferromagnetic order in nanostructured $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ is generally associated with a tetragonal distortion. This observation motivates a theoretical reassessment of the electronic structure of $\ensuremath{\gamma}\text{\ensuremath{-}}\mathrm{Fe}$ taking tetragonal distortion into account.

The results of the Labeled Release and the Gas Exchange experiments conducted on Mars by the Viking Landers show that compounds in the Martian soil can cause oxidation of organics and a release of oxygen in the presence of water. Several sources have been proposed for the oxidizing compounds, but none has been validated in situ and the cause of the observed oxidation has not been resolved. In this study, laboratory simulations of saltation were conducted to examine if and under which conditions wind abrasion of silicates, a process that is common on the Martian surface, can give rise to oxidants in the form of hydrogen peroxide ( H 2 O 2 ) and hydroxyl radicals (⋅OH). We found that silicate samples abraded in simulated Martian atmospheres gave rise to a significant production of H 2 O 2 and ⋅OH upon contact with water. Our experiments demonstrated that abraded silicates could lead to a production of H 2 O 2 facilitated by atmospheric O 2 and inhibited by carbon dioxide. Furthermore, during simulated saltation the silicate particles became triboelectrically charged and at pressures similar to the Martian surface pressure we observed glow discharges. Electrical discharges can cause dissociation of CO 2 and through subsequent reactions lead to a production of H 2 O 2 . These results indicate that the reactions linked to electrical discharges are the dominant source of H 2 O 2 during saltation of silicates in a simulated Martian atmosphere, given the low pressure and the relatively high concentration of CO 2 . Our experiments provide evidence that wind driven abrasion could enhance the reactivity of the Martian soil and thereby could have contributed to the oxidation of organic compounds and the O 2 release observed in the Labeled Release and the Gas Exchange experiments. Furthermore, the release of H 2 O 2 and ⋅OH from abraded silicates could have a negative effect on the persistence of organic compounds in the Martian soil and the habitability of the Martian surface.

Solid state physics (SSP) research at ISOLDE has been running since the mid-1970s and accounts for about 10%–15% of the overall physics programme. ISOLDE is the world flagship for the on-line production of exotic radioactive isotopes, with high yields, high elemental selectivity and isotopic purity. Consequently, it hosts a panoply of state-of-the-art nuclear techniques which apply nuclear methods to research on life sciences, material science and bio-chemical physics. The ease of detecting radioactivity—, We gratefully acknowledge many years of support given to the maintenance and upgrade of the solid state physics laboratories and provision of large scale equipment by the Federal Ministry of Education and Research (BMBF) through different grants, including 05K13TSA and 05K16PGA, from Fundacao para a Ciencia e a Tecnologia (FCT) project CERN-FIS-NUC-0004-2015 and Research Foundation Flanders (FWO) in collaboration with the University of Leuven (KU Leuven). ASF acknowledges the PhD grants support by FCT (SFRH/BD/84743/2012) and KU Leuven. ED-B and ARGC acknowledge FCT-PhD grants (SFRH/BD/95865/2013 and SFRH/BD/86386/2012.

The common charge states of Sn are 2+ and 4+. While charge neutrality considerations favour 2+ to be the natural charge state of Sn in ZnO, there are several reports suggesting the 4+ state instead. In order to investigate the charge states, lattice sites, and the effect of the ion implantation process of dilute Sn atoms in ZnO, we have performed 119Sn emission Mossbauer spectroscopy on ZnO single crystal samples following ion implantation of radioactive 119In (T ½ = 2.4 min) at temperatures between 96 K and 762 K. Complementary perturbed angular correlation measurements on 111mCd implanted ZnO were also conducted. Our results show that the 2+ state is the natural charge state for Sn in defect free ZnO and that the 4+ charge state is stabilized by acceptor defects created in the implantation process.

Hydrothermally synthesized LiFePO4 has been prepared with different synthesis times in order to study defects in the crystal structure and their evolution. The Mossbauer spectra can be interpreted as due to three components, Fe2+ in LiFePO4, Fe2+ in unreacted precursor material which resembles the Mossbauer spectrum of Fe2+ in vivianite (Fe3(PO4)2·8H2O) and Fe3+. The Fe3+ contribution differs from room temperature oxidation of the precursor material, and can partly be due to charge compensating defects in the LiFePO4 structure. With increasing synthesis time, the latter two contributions virtually disappear from the spectra.

Mossbauer spectra of samples from the 2010 Fimmvorðuhals/Eyjafjallajokull eruption are presented with determinations of the Fe3 + /FeTot ratios. Mossbauer spectra of time series of samples from the Eyjafjallajokull eruption show a change in the characteristics of the erupted material mid-way in the eruption, suggesting changing access of water to the eruption.

The crystal structure and defect chemistry of hydrothermally synthesized LiFe1-xMnxPO4 (x = 0, 0.25, and 0.50) particles have been characterized by simultaneous neutron and X-ray Rietveld refinement as well as X-ray and neutron pair distribution function (PDF) analysis, crystallinity determination, Mossbauer spectroscopy, ion coupled plasma (ICP) studies, and scanning electron microscopy (SEM). The very detailed structural refinements show that fast hydrothermal synthesis causes partial Fe-occupancy and vacancies on the Li (M1) site, while the Fe (M2) site is always fully occupied by iron. Thus, the defect is not merely a Li/Fe antisite defect, and excessive amounts of Fe are the origin of the disorder in the structure. Neutron and X-ray total scattering with PDF analysis show that after fast hydrothermal synthesis, the crystalline, defective LixFeyPO4 coexists with amorphous Li/Fe-PO4 structures having just short-range order. Iron excess is only seen in the crystalline part of the particles, and as the c...

Emission Mossbauer Spectroscopy (eMS) measurements, following low fluence (

Using spreadsheet programs to analyse spectral data opens up new possibilities in data analysis. The spreadsheet program contains all the functionality needed for graphical support, fitting and post processing of the results. Unconventional restrictions between fitting parameters can be set up freely, and simultaneous analysis i.e. analysis of many spectra simultaneously in terms of model parameters is straightforward. The free program package Vinda – used for analysing Mossbauer spectra – is described. The package contains support for reading data, calibration, and common functions of particular importance for Mossbauer spectroscopy (f-factors, second order Doppler shift etc.). Methods to create spectral series and support for error analysis is included. Different types of fitting models are included, ranging from simple Lorentzian models to complex distribution models.

The lattice sites, valence states, resulting magnetic behaviour and spin-lattice relaxation of Fe ions in GaN and AIN were investigated by emission Mossbauer spectroscopy following the implantation of radioactive Mn-57(+) ions at ISOLDE/CERN. Angle dependent measurements performed at room temperature on the 14.4 keV gamma-rays from the Fe-57 Mossbauer state (populated from the Mn-57/beta(-) decay) reveal that the majority of the Fe ions are in the 2+ valence state nearly substituting the Ga and Al cations, and/or associated with vacancy type defects. Emission Mossbauer spectroscopy experiments conducted over a temperature range of 100-800 K show the presence of magnetically split sextets in the "wings" of the spectra for both materials. The temperature dependence of the sextets relates these spectral features to paramagnetic Fe3+ with rather slow spin-lattice relaxation rates which follow a T-2 temperature dependence characteristic of a two-phonon Raman process. (C) 2015 Elsevier B.V. All rights reserved.

The mixed-valence complex Fe3 O(cyanoacetate)6 (H2 O)3 (1) has been studied by single-crystal X-ray diffraction analysis at pressures up to 5.3(1) GPa and by (synchrotron) Mossbauer spectroscopy at pressures up to 8(1) GPa. Crystal structure refinements were possible up to 4.0(1) GPa. In this pressure range, 1 undergoes two pressure-induced phase transitions. The first phase transition at around 3 GPa is isosymmetric and involves a 60° rotation of 50 % of the cyanoacetate ligands. The second phase transition at around 4 GPa reduces the symmetry from rhombohedral to triclinic. Mossbauer spectra show that the complex becomes partially valence-trapped after the second phase transition. This sluggish pressure-induced valence-trapping is in contrast to the very abrupt valence-trapping observed when compound 1 is cooled from 130 to 120 K at ambient pressure.

Emission Mössbauer Spectroscopy following the implantation of radioactive precursor isotope $^{57}$Mn$^{+}$ (T$_{1/2}$= 1.5 min) into ZnO single crystals at ISOLDE/CERN shows that a large fraction of $^{57}$Fe atoms produced in the $^{57}$Mn beta decay is created as paramagnetic Fe$^{3+}$ with relatively long spin-lattice relaxation times. Here we report on ZnO pre-implanted with $^{56}$Fe to fluences of 2×10$^{13}$, 5×10$^{13}$ and 8 × 10$^{13}$ ions/cm2 in order to investigate the dependence of the paramagnetic relaxation rate of Fe$^{3+}$ on fluence. The spectra are dominated by magnetic features displaying paramagnetic relaxation effects. The extracted spin-lattice relaxation rates show a slight increase with increasing ion fluence at corresponding temperatures and the area fraction of $^{3+}$ at room temperature reaches a maximum contribution of 80(3)% in the studied fluence range.

In addition to spectral components due to Fe2 + and Fe3 + , a single line is observed in emission Mossbauer spectra following low fluence (

We present a method to describe the temperature dependence of emission Mössbauer spectra showing slow spin-lattice relaxations of Fe3 + in MgO single crystals, obtained after implantation of 57Mn at ISOLDE/CERN. The analysis is based on the Blume-Tjon model for the line-shape of relaxing paramagnetic sextets with the spin relaxation rate, ? - 1 as a parameter. The temperature dependent spin relaxation rate of Fe3 + in MgO is found to increase to ~108 s - 1 at 647 K by assuming a relaxation rate of ? - 1 < 106 s - 1 at 77 K. The results are in accordance with those obtained by electron paramagnetic resonance spectroscopy demonstrating the possibility of retrieving spin-lattice relaxation rates of dilute Fe3 + from emission Mössbauer spectroscopy of Mn/Fe-implanted oxides.

A fine grained magnetic iron oxide precipitate found in Denmark has been studied with regard to grain size, magnetic properties, aerosol transport, grain electrification, aggregation and optical reflectance. It has shown itself to be a good Martian dust analogue. The fraction of the Salten Skov I soil sample

The theory for so-called Time-Delayed-Measurements is outlined. This method allows for isothermal annealing studies in emission Mossbauer spectroscopy utilizing radioactive beams. The usefulness of this method is illustrated by the example of the annealing of a magnetic defect in ZnO.

Radioactive 57Mn+(T 1/2 = 1.5 min) ions have been implanted at the ISOLDE facility at CERN with 60 keV energy to fluences

Mossbauer spectroscopy of surface rocks, soil, and dust on Mars from the Mars Exploration Rovers (MER) suggests that the mineral olivine is widespread on the surface. Detection of the mineral by near-IR optical spectroscopy from Martian orbit indicates that it is found in relatively small isolated outcrops concentrated in the floors and rims of craters distributed around the ancient cratered highlands of Mars. To shed light on this apparent paradox, we have performed a detailed Mossbauer and visible-near-IR (VNIR) investigation of dust generated from Icelandic olivine basalt, which is a good Mossbauer analogue to the igneous rocks at Gusev crater on Mars. The results show that the amount of olivine relative to pyroxene can be underestimated by almost an order of a magnitude in VNIR reflectance spectra, most probably because of the longer effective optical path length in pyroxene compared to olivine.

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This study provides new rock magnetic and magneto-mineralogical data including Mossbauer spectroscopy of basaltic drill cores from the Stardalur volcanic complex, Iceland, in order to better understand the strong magnetic anomaly, which is caused by an extraordinary high natural remanent magnetization (NRM). NRM and magnetic susceptibility ( χ ) display a positive linear correlation ( R 2 = 0.81) and reach very high values up to 121 A/m and 148 × 10 −3 SI. Although a Curie temperature of 580 °C and a Verwey transition at about −160 °C is indicative of magnetite, χ – T heating experiments in argon and air atmosphere and thermal demagnetization measurements of NRM revealed a slight cation-deficiency. According to induced remanent magnetization experiments the remanence is carried solely by this low coercive phase. Minor titanomaghemite with a T C at about 340 °C only occurs in samples with larger oxide grains (20–80 μm). High vesicle abundances and the exsolution texture of Fe–Ti oxides suggest subaerial extrusion of the lava. A high oxygen fugacity (probably above the NNO buffer) and a low Ti/(Ti + Fe) ratio of the basaltic melt are suggested as a precondition for high concentration of magnetic minerals and therefore high primary TRM. During high temperature oxidation, ilmenite exsolution-lamellae, developed in titanomagnetite, and symplectic magnetite (+ pyroxene) formed by the breakdown of olivine. This secondary magnetite, grown at temperatures above the Curie temperature, increases the primary TRM. Early stage hydrothermal alteration (below about 375 °C) led to maghemitization of (titano)magnetite, clearly indicated by shrinkage cracks and irreversible χ – T curves. During later stage hydrothermal alteration, NRM intensity increased slightly due to the growth of secondary magnetite at lower temperatures (about 250–300 °C). This hydrothermally formed magnetite acquired only a low CRM but increased magnetic susceptibility significantly. According to our results it is suggested, that hydrothermal alteration does not necessarily lower remanent magnetization, but contributes to an increase in magnetization. The interplay of the three factors melt composition, small grain sizes of secondary magnetite due to decomposition of silicates and new formation under hydrothermal conditions caused the strong magnetic anomaly at the surface.

57Fe Mossbauer spectroscopy, following the implantation of radioactive parent 57Mn+ ions, has been performed on two chemical vapour deposited diamond samples, one synthesized in 2003 (CVD03) and the other in 2005 (CVD05). The spectra of sample CVD05 were as observed previously in natural IIa diamonds: single lines corresponding to substitutional and interstitial Fe were superimposed on a broad quadrupole split doublet. The site fraction of Fei reached 30% at 90 K. The spectra of the CVD03 sample showed, in addition to the above features, a strong contribution (>30%) from a quadrupole doublet attributable to the presence of intrinsic amorphous inclusions in the crystallites. This observation has been confirmed by X-ray diffraction.

The telltale mirror, a smooth inclined surface raised over 1 m above the deck of the Phoenix Mars Lander, was observed by the Surface Stereo Imager (SSI) several times per sol during the Phoenix Mars Lander mission. These observations were combined with a radiative transfer model to determine the thickness of dust on the wind telltale mirror as a function of time. 239 telltale sequences were analyzed and dustiness was determined on a diurnal and seasonal basis. The thickness of accumulated dust did not follow any particular diurnal or seasonal trend. The dust thickness on the mirror over the mission was 0.82 +/- 039 mu m, which suggests a similar thickness to the modal scattering particle diameter. This suggests that inclining a surface beyond the angle of repose and polishing it to remove surface imperfections is an effective way to mitigate the accumulation of dust to less than a micron over a wide range of meteorological conditions and could be beneficial for surfaces which can tolerate some dust but not thick accumulations, such as solar panels. However, such a surface will not remain completely dust free through this action alone and mechanical or electrical clearing must be employed to remove adhered dust if a pristine surface is required. The single-scattering phase function of the dust on the mirror was consistent with the single-scattering phase function of martian aerosol dust at 450 nm, suggesting that this result is inconsistent with models of the atmosphere which require vertically or horizontally separated components or broad size distributions to explain the scattering behavior of these aerosols in the blue. The single-scattering behavior of the dust on the mirror is also consistent with Hapke modeling of spherical particles. The presence of a monolayer of particles would tend to support the spherical conclusion: such particles would be most strongly adhered electrostatically. (C) 2015 Elsevier Ltd. All rights reserved.

In search for dilute magnetic semiconductors, the magnetic properties at the atomic-scale of Fe atoms incorporated in ZnO, in a concentration range of more than five orders of magnitude from 1 x 10(-5) to 2.2 at% have been probed using emission 57 Fe Mossbauer spectroscopy on implanted Mn-57 and Co-57 produced at ISOLDE/CERN. In the ultra-dilute regime (10(-5) at%), the system shows isolated paramagnetic Fe3+ ions with a spin-lattice type of relaxation. At higher concentrations (between 0.02 and 0.2 at%) a transition to spin-spin type of relaxation between neighboring Fe3+ is observed, without any signature of magnetic ordering up to 2.2 at%. Despite the many reports of dilute magnetism in 3d-doped ZnO, this atomic level study shows no evidence of any long-range magnetic ordering between isolated Fe atoms incorporated in the ZnO lattice.

We present some of the main findings from simulation studies of the Magnetic Properties Experiment on the Mars Exploration Rovers. The results suggest that the dust has formed via mechanical breakdown of surface rocks through the geological history of the planet, and that liquid water need not have played any significant role in the dust formation processes.

The general problem of finding a distribution in hyperfine interaction parameters from experimental Mossbauer spectra is outlined. Existing methods may lack flexibility to be easily applicable to simple problems. A line shape for hyperfine parameter distributions is given, which is based on linear segments in the probability function. This method is applied in the analysis of samples containing iron in a silicate glass.

The characteristics of both natural burned and experimentally burned soil profiles as seen by Mossbauer spectroscopy are described. The results help in the identification of profiles where biological and/or chemical processes may have been involved.

We report on the determination of the mineralogy of the atmospherically suspended Martian dust particles using backscattering 57Fe Mossbauer spectroscopy on dust accumulated onto the magnets onboard the Mars Exploration Rovers. The spectra can be interpreted in terms of minerals of igneous origin, and shows only limited, if any, amounts of secondary minerals that may have formed in the presence of liquid water. These findings suggest that the dust has formed in a dry environment over long time in the history of the planet.

Windborne dust is one of the most important and dynamic factors affecting the Martian surface and its atmosphere, yet there lacks a detailed physical understanding how it is transported. We present a miniature laser-based optoelectronic instrument for use on a Mars lander. It integrates sensors capable of quantifying important parameters needed for the understanding and modeling of dust transport on Mars, these include wind speed, wind direction, suspended dust concentration, dust deposition and removal rates as well as the electrification of the Martian dust. Dust electrification has been seen from experimental simulations to be of considerable importance to the processes of adhesion and cohesion, specifically prompting the formation of low mass density dust aggregates. Testing of this prototype instrument has been performed under simulated Martian conditions in a wind tunnel facility. The results and analysis of its functionality will be presented.

We report on the detection of Fe i −B pairs in heavily B doped silicon using 57Fe emission Mossbauer spectroscopy following implantation of radioactive 57Mn+ parent ions (T 1/2=1.5 min) at elevated temperatures >850 K. The Fe i −B pairs are formed upon the dissociation of Fe i −V pairs during the lifetime of the Mossbauer state (T l/2=100 ns). The resulting free interstitial Fei diffuses over sufficiently large distances during the lifetime of the Mossbauer state to encounter a substitutional B impurity atom, forming Fe i −B pairs, which are stable.up to ∼1,050 K on that time scale.

Motivated by questions raised by the magnetic properties experiments on the NASA Mars Pathfinder and Mars Exploration Rover (MER) missions, we have studied in detail the capture of airborne magnetic dust by permanent magnets using a computational fluid dynamics (CFD) model supported by laboratory simulations. The magnets studied are identical to the capture magnet and filter magnet on MER, though results are more generally applicable. The dust capture process is found to be dependent upon wind speed, dust magnetization, dust grain size and dust grain mass density. Here we develop an understanding of how these parameters affect dust capture rates and patterns on the magnets and set bounds for these parameters based on MER data and results from the numerical model. This results in a consistent picture of the dust as containing varying amounts of at least two separate components with different physical properties.

The cover shows part of the Larry's Lookout panorama, seen from the Mars Exploration Rover (MER) Spirit during its drive up Husband Hill: the summit is about 200 metres from the rover. Six papers this week report in detail on the MER mission. An Analysis compares predictions used to select a landing site with the conditions actually encountered. This ‘ground truth’ will be invaluable for interpreting future remote-sensing data. Surface chemistry suggests that the upper layer of soil may contain 1% meteoritic material. MER provides a unique glimpse of solar transits of the moons Phobos and Deimos. Rover Opportunity examined wind-related processes, and spectroscopy indicates a dry origin for atmospheric dust. Features from within the Gusev crater give more information on the role of liquid water in Mars's past. An accompanying News and Views puts the MER data in context. The ubiquitous atmospheric dust on Mars is well mixed by periodic global dust storms, and such dust carries information about the environment in which it once formed and hence about the history of water on Mars1. The Mars Exploration Rovers have permanent magnets to collect atmospheric dust for investigation by instruments on the rovers2,3. Here we report results from Mossbauer spectroscopy and X-ray fluorescence of dust particles captured from the martian atmosphere by the magnets. The dust on the magnets contains magnetite and olivine; this indicates a basaltic origin of the dust and shows that magnetite, not maghemite, is the mineral mainly responsible for the magnetic properties of the dust. Furthermore, the dust on the magnets contains some ferric oxides, probably including nanocrystalline phases, so some alteration or oxidation of the basaltic dust seems to have occurred. The presence of olivine indicates that liquid water did not play a dominant role in the processes that formed the atmospheric dust.

X-ray analysis with the instruments on the rovers on Mars, landed in January 2004, and application to the thin dust layer accumulated on magnets on the rovers are discussed. Particle excitation and x-ray fluorescence have different effective depths and call for a more elaborate analysis of a thin surface layer. Measurements from Mars are presented and exhibit a similar elemental composition of the accumulated magnetic dust to that of the surrounding soil.

Radioactive 57Mn isotopes have been implanted into Si1−xGex crystals (x ≤ 0.1) at elevated temperatures for Mossbauer studies of the diffusion of interstitial 57Fe daughter atoms. The atomic jump frequency is found to increase upon Ge alloying. This is attributed to a lowering of the activation energy, i.e. the saddle point energy at hexagonal interstitial sites with Ge neighbour atoms.

Suspended dust is a dominant component of the Martian environment. It has a major influence on atmospheric circulation and it is deposited widely over the planetary surface causing a serious hazard to instrumentation. In order to study dust transport, quantification of the wind flow and dust concentration are vital. A simple laser-based anemometer system is presented that is able to measure suspended dust grain velocity and turbulence from a landed spacecraft. This system has advantages over other techniques of wind speed determination in being insensitive to contamination or atmospheric conditions such as temperature, pressure or composition. For the first time it would allow direct measurement of the suspended dust concentration on Mars. A prototype instrument has been constructed and successfully tested in a wind tunnel facility under simulated Martian conditions. The optics are simple in design, light weight and the instrument has low power consumption. It is also robust and the output signal is easily interpreted, producing only a small data volume. Future improvements will be discussed, specifically modification to measure wind direction, the possibility of obtaining information about dust grain size and the construction of a flight model.

A new optical instrument has been developed to precisely measure the local accumulation of dust particles on a surface. This device can be used in combination with applied magnetic or electric fields in order to investigate physical properties of the dust and its interactions with the surface. In this prototype instrument, permanent magnets were used to capture suspended magnetic dust in a Mars simulation wind tunnel. The scientific objectives that may be addressed with such a device are discussed.

The Fe oxide mineralogy behind the reddish colour (up to Munsell 10R) of a soil and four Quaternary surface deposits from central Jutland (Denmark) was investigated by XRD, TEM, Mossbauer spectroscopy and bulk saturation magnetization. The red soil (Naesset) consists of a 1 m deep patch, ~10 m 2 in area. It is one of at least 5–10 isolated spots of limited size which contain hematite and maghemite, and are probably due to local fire. The four more extended (several hundred m 2 ) red sediments (Salten Skov, Salten, Pot Molle and Laasby) all occur at the feet of slopes and formed from Fe 2+ -containing seepage water. They contain 25– ~100% Fe oxides, originally consisting of ferrihydrite. The well-drained parts of the deposits are at present all dominated by goethite. Hematite and maghemite were also identified at two sites in the top ~25 cm, one site containing goethite and hematite and probably a little maghemite, and the other goethite and probably hematite. The presence of hematite and particularly maghemite in the surface sediments could be explained by heating of goethite. However, there is no historic or prehistoric evidence of heating activity, and the spatial extension is much wider than that of normal human events. In contrast to the burned soil site, goethite is still present in the upper layers together with a high content of organic matter. Thus, although the present belief is that the deposits formed by heating, site evidence is to the contrary.