Haraldur Páll Gunnlaugsson

KU Leuven | ku leuven · Department of Physics and Astronomy

Emission 57 Fe Mössbauer spectroscopy (eMS), following the implantation of radioactive 57 Mn + ions, has been used to study the temperature dependence of the hyperfine magnetic field at Fe sites in Ba-doped BiFeO 3 (BFO) thin films. 57 Mn β decays (t 1/2 = 90 s) to the 14.4 keV Mössbauer state of 57 Fe, thus allowing online eMS measurements at a se...

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 magnetoele...

There is an apparent mismatch between electron paramagnetic resonance and Mössbauer spectroscopy results on the charge and spin states of dilute Fe impurities in NaCl; Mössbauer spectroscopy data have been interpreted in terms of high-spin Fe 2+ , while electron paramagnetic resonance studies suggest low-spin Fe 1+. In the present study, the charge...

Charge states and lattice sites of Fe ions in virgin and Mn-doped Al x Ga 1- x N samples were investigated using ⁵⁷ Fe emission Mössbauer spectroscopy following radioactive ⁵⁷ Mn ⁺ ion implantation at ISOLDE, CERN. In the undoped Al x Ga 1- x N, Fe ²⁺ on Al/Ga sites associated with nitrogen vacancies and Fe ³⁺ on substitutional Al/Ga sites are iden...

The magnetic properties of the Fe/V superlattices were studied by conventional Conversion Electron Mössbauer Spectroscopy (CEMS) and online 57Fe+ emission Mössbauer Spectroscopy (eMS) at room temperature (RT) at ISOLDE/CERN. The unique depth-enhanced sensitivity and ultradiluted regime of the probe atoms adopted in this eMS facility enabled the inv...

Van der Waals α-MoO3 samples offer a wide range of attractive catalytic, electronic, and optical properties. We present herein an emission Mössbauer spectroscopy (eMS) study of the electric-field gradient (EFG) anisotropy in crystalline free-standing α-MoO3 samples. Although α-MoO3 is a two dimensional (2D) material, scanning electron microscopy sh...

The magnetic properties of Mn x Ga alloys critically depend on composition x, and the atomic‐scale origin of those dependences is still not fully disclosed. Molecular beam epitaxy has been used to produce a set of Mn x Ga samples (x = 0.7 ÷ 1.9) with strong perpendicular magnetic anisotropy, and controllable saturation magnetization and coercive fi...

An extension of the online implantation chamber used for emission Mössbauer 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 combin...

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 exa...

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 Mössbauer spectroscopy (eMS) followin...

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 ad...

In this study we report on the results from emission $^{57}$Fe M${\"o}$ssbauer Spectroscopy experiments, using dilute $^{57}$Mn implantation into pristine (TiO$_2$) and hydrogenated anatase held at temperatures between 300-700 K. Results of the electronic structure and local environment are complemented with ab-initio calculations. Upon implantatio...

Performance of TiO2-based materials is highly dependent on the electronic structure and local defect configurations. Hence, a thorough understanding of defects interaction plays a key role. In this study we report on the results from emission ⁵⁷Fe Mössbauer Spectroscopy experiments, using dilute ⁵⁷Mn implantation into pristine (TiO2) and hydrogenat...

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 Mössbauer Spectroscopy (eMS) following implantation of ⁵⁷Mn (T½ = 1.5 min). The Mössbauer spectra analysis reveal high spin Fe³⁺ ions substituted on both the octahedral and t...

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 l...

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 ul...

Correlations were established between the hyperfine field distribution around the Fe atoms, the multiferroic properties, and the high magnetoelectric coef- ficients in BaTiO3-BiFeO3 multilayer stacks with variable BiFeO3 single layer thickness, down to 5 nm. Of key importance in this study was the deposition of ⁵⁷Fe - enriched BiFeO3, which enhance...

The underlying mechanism driving the structural amorphous-to-crystalline transition in Group VI chalcogenides is still a matter of debate even in the simplest GeTe system. We exploit the extreme sensitivity of ⁵⁷Fe emission Mössbauer spectroscopy, following dilute implantation of ⁵⁷Mn (T1/2 = 1.5 min) at ISOLDE/CERN, to study the electronic charge...

γ−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 γ−Fe nanop...

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...

Solid State 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 tec...

We describe an experimental setup for conversion electron Mössbauer spectroscopy (CEMS) at low temperature. The setup is composed of a continuous flow cryostat (temperature range of 4.2-500 K), detector housing, three channel electron multipliers, and corresponding electronics. We demonstrate the capabilities of the setup with CEMS measurements per...

Room temperature magnetoelectric BiFeO3-BaTiO3superlattices with strong out-of-plane magnetic anisotropy have been prepared by pulsed laser deposition. We show that the out-of-plane magnetization component increases with the increasing number of double layers. Moreover, the magnetoelectric voltage coefficient can be tuned by varying the number of i...

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 <...

57Fe emission Mössbauer spectroscopy has been applied to study the lattice location and properties of Fe in gadolinium gallium garnet Gd3Ga5O 12 (GGG) single crystals in the temperature interval 300 – 563 K within the extremely dilute (<10−4 at.%) regime following the implantation of57Mn (T 1/2= 1.5 min.) at ISOLDE/CERN. These results are compared...

Deposition of volcanic ash from explosive eruptions to the surface ocean is a source of iron (Fe) to 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) an...

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) Mössbauer 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 t...

Emission Mössbauer Spectroscopy (eMS) measurements, following low fluence (<1012 cm−2) implantation of 57Mn (t 1/2 = 1.5 min.) into ZnO single crystals pre-implanted with Ar and C ions, has been utilized to test the sensitivity of the 57Fe eMS technique to the different types of defects generated by the different ion species. The dominant feature o...

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...

Emission Mössbauer spectroscopy has been utilised to characterize dilute 57Fe impurities in In 2O3 following implantation of 57Mn (T 1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In 3+, however the spectra are dominated by spectral lines due to pa...

Emission Mössbauer Spectroscopy following the implantation of radioactive precursor isotope 57Mn+ (T 1/2= 1.5 min) into ZnO single crystals at ISOLDE/CERN shows that a large fraction of 57Fe atoms produced in the 57Mn beta decay is created as paramagnetic Fe3+ with relatively long spin-lattice relaxation times. Here we report on ZnO pre-implanted w...

The lattice sites, valence states, resulting magnetic behaviour and spin-lattice relaxation of Fe ions in GaN and AlN were investigated by emission Mössbauer spectroscopy following the implantation of radioactive 57Mn+ ions at ISOLDE/CERN. Angle dependent measurements performed at room temperature on the 14.4 keV γ-rays from the 57Fe Mössbauer stat...

The atmosphere and surface of Mars both derive their characteristic colour from the presence of fine micron-sized dust. The two reservoirs are linked with the breakdown of surface materials creating the fine particulates that are lofted and redistributed across the planet. These particulates subsequently accumulate once again where atmospheric cond...

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 fi ve orders of magnitude from 1 × 10 −5 to 2.2 at% have been probed using emission 57 Fe Mössbauer spectroscopy on implanted 57 Mn and 57 Co produced at ISOLDE/CERN. In the ultra-dilute re...

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 f...

57Fe Emission Mössbauer spectra obtained after low fluence (<1012 cm −2) implantation of 57Mn (T 1/2= 1.5 min.) into ZnO single crystal held at temperatures below room temperature (RT) are presented. The spectra can be analysed in terms of four components due to Fe 2+ and Fe 3+ on Zn sites, interstitial Fe and Fe in damage regions (Fe D ). The Fe...

Isolated 57Fe atoms were studied in MgO single-crystals by emission M€ossbauer spectroscopy following implantation of 57Mn decaying to 57Fe. Four M€ossbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe2þ and Fe3þ, respectively; a third co...

A study of the annealing processes and charge state of dilute Fe in rutile TiO2 single crystals was performed in the temperature range 143–662 K, utilizing online 57Fe emission Mössbauer spectroscopy following low concentrations (<10−3 at%) implantation of 57Mn (T1/2 = 1.5 min). Both Fe3+ and Fe2+ were detected throughout the temperature range. Thr...

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, Mössbauer spectroscopy, ion coupled plasma (ICP) s...

Fe Mössbauer spectroscopy - a versatile technique involving the recoil-free, resonant absorption and emission of nuclear gamma (γ) rays by the iron-57 isotope in natural iron in solids - has been used to provide quantitative information about the mineral host, occupation sites and oxidation states of iron atoms in geological samples. This technique...

In addition to spectral components due to Fe2 + and Fe3 + , a single line is observed in emission Mössbauer spectra following low fluence (<1015 cm − 2) implantation of 57Fe*, 57Mn and 57Co in α-Al2O3. For the 57Co and 57Mn implantations, the intensity of the single line is found to depend on the emission angle relative to the crystal symmetry axis...

Introduction Tumbling experiments with quartz sand with the purpose of tracing the effect of broken bonds in mineral surfaces resulted in an unexpected production of aggregates. These aggregates are a few microns in diameter, spherical and resembling tiny white "snowballs." Particle comminution by aeolian and other natural weathering processes are...

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 Fe3 + /Fe2 + ratio shows a marked increase. It is suggested that this annealing stage is due to the dissociat...

Hydrothermally synthesized LiFePO4 has been prepared with different synthesis times in order to study defects in the crystal structure and their evolution. The Mössbauer spectra can be interpreted as due to three components, Fe2+ in LiFePO4, Fe2+ in unreacted precursor material which resembles the Mössbauer spectrum of Fe2+ in vivianite (Fe3(PO4)2·...

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

The influence of the ion implantation process on the charge state of dilute (57)Fe impurities implanted as radioactive (57)Mn in ZnO is investigated by (57)Fe emission Mössbauer spectroscopy. One sample is additionally implanted with stable (23)Na impurities. Both Fe(2+) and Fe(3+) charge states are observed, and the Fe(3+)/Fe(2+) ratio is found to...

Several related aspects of Aeolian activity are presently being studied in the laboratory, the most recent advances in this field will be presented. These include simulating wind driven erosion in the laboratory, quantifying erosion rates and the study of mineral change due to mechanical activation. Also advances in our understanding of the electri...

The annealing of defects in Sb/Sn implanted diamond has been studied in 119Sn Mössbauer spectroscopy following the implantation of radioactive parent isotopes 119Xe and 119mSn. Our results show that after annealing above 1300K, 40% of the implanted ions are located at or near regular sites in the lattice. Significant implantation induced defects ho...

We have applied implantation of radioactive 57Mn + (T1/2 = 1.5 min) at the ISOLDE facility at CERN with 50–60 keV energy to fluences <1012 /cm2 to study the emission Mössbauer spectra from the 14.4 keV transition of the 57Fe daughter atoms. For fluences ≥5 × 101157Mn/cm2, the spectra are dominated by the Fe3 + state exhibiting a slow paramagnetic r...

At a number of sandy soil sites in Mid Jutland, Denmark, with iron content of 1-2%, very red spots (Munsell colour: dusky red 10R 3/4) of a few square meters are found. These spots are most likely due to burning events. After the fire ashes raised pH. This dispersed silt and clay size soil particles which were then transported with seepage water do...

The 2010 Eyjafjallajökull summit eruption (Iceland) produced large amounts of fine ash, disturbing air traffic across the North-Atlantic and within Europe. Mössbauer spectroscopy of ash-samples and a lava-bomb has been performed to study the material properties and to gain insight into why the volcano produced so vast amounts of fine grained materi...

A Nordic Semiconductor Meeting is held every other year with the venue rotating amongst the Nordic countries of Denmark, Finland, Iceland, Norway and Sweden. The focus of these meetings remains 'original research and science being carried out on semiconductor materials, devices and systems'. Reports on industrial activity have usually featured. The...

The spin–lattice relaxation rate of paramagnetic Fe 3+ in single-crystalline ZnO has been determined following low-fluence (< 10 12 cm −2) 60 keV implantation of 57 Mn + (T 1/2 = 1.5 min) and emission Mössbauer spectroscopy on the 57 Fe daughter nucleus in the temperature range from 300 to 664 K. The spin–lattice relaxation of Fe 3+ is found to fol...

119Sn Mössbauer measurements have been made on a 3C-SiC single crystal implanted with 60 keV precursor radioactive 119In ∗ ions at ISOLDE/CERN. Spectra collected at sample temperatures of 300–670 K have been analysed in terms of two single lines and a quadrupole split doublet, which based on their isomer shifts are assigned respectively to Sn ions...

Conversion electron Mössbauer Spectroscopy measurements have been made on ZnO single crystals implanted with 60 keV 57Fe to 4 and 8 at.% peak concentrations, and annealed up to 800°C. The spectra show quite strong changes with annealing, but no evidence of magnetic components, thus precluding the formation of large sized precipitates or secondary p...

The electrification of wind-blown dust grains was studied in a series of laboratory experiments to examine how grain electrification depends on grain size, grain mineralogy, atmospheric composition, atmospheric pressure, and the method of dust dispersal. This work is intended to contribute to a deeper physical understanding of particle electrificat...

The lattice locations and electronic configurations of Fe in 57Co/57Fe implanted ZnO (to (5‐6) × 1014 Fe/cm-2) have been studied by 57Fe Mössbauer emission spectroscopy. The spectra acquired upon room temperature implantation show ∼20% of the probe atoms as Fe2+ on perturbed Zn sites and the remaining fraction as Fe2+ in damage sites of interstitia...

The Mars Simulation wind tunnel at Aarhus University is a unique ESA and EU supported simulation facility designed for studies of the Martian environment. Specifically it is capable of recreating the key physical parameters such as temperature, pressure (composition), wind flow and importantly the suspension of dust particulates. This facility is a...

The wind driven transport of granular material is an important environmental/climatic factor on Earth and even more so on Mars. Several related aspects of Aeolian activity are presently being studied in the laboratory. These include simulating wind driven erosion in the laboratory and the study of mineral change due to mechanical activation as well...

Experiments on magnetite (Fe3O4) to produce hematite (Fe2O3) under martian conditions are reported. Water and atmospheric oxygen are not involved in oxidation. The findings represent a putative mechanism for the reddish color of Mars.

Basal ice at the margin of the Greenland ice sheet was studied with respect to its physical characteristics and microbiological community. The basal ice contained high concentrations of dissolved ferrous Fe and must therefore be anoxic. Oxygen consumption experiments indicate that 50% of the oxidation was due to biological activity while the rest c...

Here we present a novel mechanism for mineral alteration which might still be active at the surface of Mars today. The mechanism involves the wind induced transport (saltation) of sand which leads not only to erosion, but also activation of mineral grain surfaces followed by chemical reaction (for example oxidation). Previous laboratory work has de...

Prompted by the generally poor understanding of the nature of magnetic phenomena in 3d-metal doped ZnO, we have undertaken on-line (57)Fe Mossbauer spectroscopy on ZnO single crystals in an external magnetic field of 0.6 T, following the implantation of radioactive (57)Mn ions at room temperature. The Mossbauer spectra of the dilute Fe impurities a...

Laboratory simulations are an invaluable complement to in-situ observations from extreme environments such as Mars, this is true for science as well as technology. Together with Aarhus University in Denmark, the European Space Agency has developed this facility as the most advanced Mars-environment simulator.

All planets/moons with an atmosphere can generate surface winds which can lead to the transport of material and generate surface erosion, producing sand and sand form, forming dust and generating atmospheric dust aerosols. These processes actively restructure the planetary surface and can change its mineralogy. Although the physical processes are b...

The Magnetic Properties Experiment (referred to as iSweep or Caltarget) onboard the Phoenix lander was executed in the arctic region of Mars during the mission's 152 sols lifetime. The iSweep experiment involved periodic multispectral imaging of a series of permanent ring magnets. It was designed to attract airborne magnetic dust particles to certa...

The valence state and annealing reactions of Mn/Fe in single crystalline α-Al2O3 have been determined following low fluence (<1012cm − 2) 60keV implantations of 57Mn +  (T1/2 = 1.5min) and emission Mössbauer spectroscopy on the 57m Fe daughter nuclei in the temperature range from 110–700K. At 110K, most probe atoms are found in the Fe2 +  state in...