Relaxation behaviour of Co and Ni implanted into MgO (original) (raw)
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Magnetic nanoscale aggregates of cobalt and nickel in MgO single crystals
The European Physical Journal B, 2005
The magnetic properties of Co and Ni nanosized aggregates formed after implantation of nickel and cobalt ions in magnesium oxide single crystals were investigated. The influence of the implantation energy and annealing treatments was characterized. The particle size distribution was determined from the combined analysis of the magnetic moment dependence on both magnetic field and temperature, and used to determine the magnetic anisotropy constant of the aggregates. The results for nickel aggregates indicate the presence of an antiferromagnetic layer after the annealing treatments.
Magnetic behavior of Co and Ni implanted MgO
Journal of Magnetism and Magnetic Materials, 2004
Single crystals of MgO were implanted with high doses of Co and Ni ions, aiming at the possibility of producing colloidal dispersions of metallic precipitates. Post-implantation annealing in vacuum is used to promote the diffusion of the implanted ions and the recovery of the MgO lattice. Results of magnetization measurements as a function of temperature and magnetic field are presented and correlated with information obtained by Rutherford backscattering measurements in the same samples.
International Journal of Engineering, 2020
Pure and doped magnesium oxide nanoparticles were successfully synthesized employing a sol-gel process. The synthesized nanoparticles were characterized by thermal differential analysis, X-ray powder diffraction, transmission electron microscopy, scanning electron microscope, energy-dispersive X-ray spectroscopy, and vibrating sample magnetometer. X-ray diffraction patterns confirmed the crystallization of MgO structure and correspondingly ratified that the transition metal atoms were incorporated into the MgO host lattice. The crystallite size decreases as the concentration of dopants were augmented. TEM images showed that the particles of pristine magnesium oxide were embedded in the sheet matrix of the graphene-like layer with a size of 22.06 nm. The EDS spectra revealed the presence of carbon in pure MgO nanoparticles, while nickel and chromium were distributed in the host lattice. Based on VSM measurements, room temperature ferromagnetism in pristine MgO-NPs could be ascribed to the presence of either Mg vacancy or carbon atoms. Furthermore, paramagnetic ordering had been observed upon doping. Overall, the prepared MgO-NPs may be found as a potential application in spintronics devices.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2002
In studies on the controlled growth of metallic precipitates in MgO it is attempted to use nanometer size cavities as precursors for formation of metallic precipitates. In MgO nanocavities can easily be generated by light gas ion bombardment at room temperature with typically 30 keV ion energy to a dose of 10 16 cm À2 , followed by annealing to 1300 K. It has been shown earlier by transmission electron microscopy (TEM) that the cavities (thickness 2-3 nm and length/ width 5-10 nm) have a perfectly rectangular shape bounded by {1 0 0} faces. The majority of the gas has been released at this temperature and the cavities are stable until annealing at 1500 K. The depth location of the cavities and the implanted ions is monitored by positron beam analysis, neutron depth profiling, RBS/channeling and energy dispersive spectroscopy. The presence of metallic nanoprecipitates is detected by optical absorption measurements and by highresolution XTEM. Surprisingly, all the metallic implants induce, in addition to metallic precipitates in a band at the mean ion range, small rectangular and cubic nanocavities. These are most clearly observed at a depth shallower than the precipitate band. In the case of gold the cavities are produced in close proximity to the crystal surface. The results indicate that in MgO vacancy clustering dominates over Frenkel-pair recombination. Results of molecular dynamics calculations will be used to discuss the observed defect recovery and clustering processes in MgO. Ó
Cobalt and Iron Ions in MgO Nanocrystals: Should They Stay or Should They Go
The Journal of Physical Chemistry C, 2019
Identification and manipulation of transition metal ion impurities in oxide nanoparticles require an in-depth understanding of their stability, segregation behavior and, at the same time, knowledge about their surface reactivity. Powders of magnesium oxide nanoparticles with admixtures of iron or cobalt ions, as two next neighbors in the periodic table, were synthesized in the gas phase via injection of metal organic precursors into the magnesium combustion flame followed by temperature quenching of resulting nanocrystals in argon. In these model systems of cubic nanocrystals, we explored the distinct stability of these impurities in great detail. While Co 2+ ions keep their divalent valence state and substitute the host ions in the cationic sublattice, Fe 3+ ions emerge due to the energy gain provided by charge compensation and impurity-vacancy complex formation. The very different behavior of Co and Fe ions in the MgO host lattice, their changes in the local environment and the different trends in segregation have been investigated by means of X-ray absorption and photoelectron spectroscopies and structure characterization techniques. Abundance and energetics of the defects and defect complexes were determined within the framework of density functional theory and enabled us to explain consistently the reported experimental observations. Oxidation state and nature of the defects cluster have a significant impact on particle size and annealing induced morphology evolution, which determine their materials properties as components in heterogeneous catalysis and functional ceramics.
Undoped and cobalt doped MgO nanoparticles (Mg 1-x Co x O, x = 0, 0.03, 0.06 and 0.12) were prepared by co-precipitation method. The synthesized samples were characterized by using X-ray diffraction (XRD), differential thermal analysis (DTA) and Ultraviolet-Visible (UV-Vis) spectroscopy. The UV-Visible absorption spectra showed a redshift with the increase in cobalt doping content in MgO host lattice while corresponding bandgap energy of cobalt doped MgO-NPs was decreased with the increase of doping concentration. The XRD patterns revealed the formation of rock salt MgO phase nanostructures. The Rietveld analysis revealed the formation of impurity phase (Co 3 O 4 ), which was remarkably appear at higher doping concentration (x = 0.12). Rietveld refinement was utilized to investigate the individual influences of coherent domain sizes and lattice strain on the peak broadening of the pure and cobalt doped MgO-NPs. The coherent domain size increased from 7.44 nm to 8.11 nm with increasing Co doping amount up to x = 0.06. The strain decreased with increasing in cobalt content. The decreasing trend in lattice constant "a" was observed with increasing doping concentration which confirms the incorporation of Co ions into the MgO host lattice. Furthermore, the linear and planar defects were also considered. First-principles calculations based on DFT were employed to determine elastic constants for the pure and doped MgO. These values were then used in combination with X-ray diffraction data to measure stacking fault energies as a function of doping concentration. The results showed that the stacking fault energy decreased as the doping concentration increase. The formation enthalpy and bonding properties of the studied compounds were also inspected. Further, the magnetic features of Co monodoping and (Co, Mg or O vacancy) co-doping in MgO host lattice were studied. The results reveal that the studied compounds may have potential applications in spintronics and magnetic data storage.
A comparative study on magnesium hydroxide and magnesium oxide nanostructures
DAE SOLID STATE PHYSICS SYMPOSIUM 2018
Mg(OH) 2 andMgO nano particles having flake, like morphology have been synthesized using hydrothermal method.XRD pattern revealed the formation of hexagonal phase for Mg(OH) 2 while cubic phase for MgO. SEM images shows the transformation of morphology from nanoflakes to nanoballs like shape upon change in crystal structure from hexagonal Mg(OH) 2 tocubicMgO. Thermal decomposition and percentage weight loss were calculated through thermogravimetric analysis (TGA) and it is inferred that defects related to oxygen vacancies are responsible for the magnetic propertiesand the origin of d 0 ferromagnetism in these non-magnetic oxides.
Journal of Alloys and Compounds, 2019
The magnetic properties of MgO thin films were discussed as an interplay among the oxygen vacancies, Mg 2þ ion coordination and structural order deposited using radio frequency (RF) sputtering method by varying substrate temperature and deposition power followed by in-situ annealing. Rutherford backscattering spectrometry (RBS) and high resolution transmission electron microscopic (HRTEM) performed for these films showed decrease of film thickness with increase of substrate temperature. Films are thicker for higher sputtering powers at corresponding substrate temperatures. Spectral features in Mg K-edge near edge X-ray absorption fine structure (NEXAFS) spectra are characteristics of MgO for both sputtering powers at substrate temperature of room temperature (RT) and 350 C. O K-edge NEXAFS spectra exhibited onset of oxygen vacancies as inferred from pre-edge region. Magnetization versus applied magnetic field curves for these films showed onset of d o ferromagnetism. This behavior ceased with increase of substrate temperature, however, become dominant with increase of sputtering power. Magnetic behavior was dominant for the films which had slightly distorted Mg 2þ ion coordination. The existence of oxygen vacancies was not observed to be consistent with magnetization. Thus, this study envisaged the role of Mg 2þ ion coordination, long range structural order and oxygen vacancies in order to determine magnetism in these systems.
Stability and Local Environment of Iron in Vapor Phase Grown MgO Nanocrystals
The Journal of Physical Chemistry C, 2017
Metallocene injection into a metal combustion flame has been used for trapping transition metal ions inside MgO nanocrystals. Vacuum annealing changes the properties of resulting nonequilibrium solids towards thermodynamic equilibrium and provides means to control impurity localization and, as a result, the nanomaterials' functional properties. By combining structure characterization (X-ray diffraction and Transmission Electron Microscopy) with X-ray absorption spectroscopy and Mössbauer measurements, we tracked valence state and local chemical environment changes of Fe 3+ ions inside vapor phase synthesized MgO nanocrystals. At a concentration of (1.5 ± 0.2) at-% Fe about (1400 ± 200) Fe 3+ ions are effectively diluted within 12 nm sized nanocubes, where they form Fe 3+-Mg 2+ vacancy complexes. Increase of the iron concentration produces additional effects: enhanced ion diffusion and particle coarsening at elevated temperatures, clustering of Fe 3+-Mg 2+ vacancy complexes and, after annealing to T = 1173 K, the nucleation of a magnesioferrite phase that can be detected by X-ray diffraction for 4 at-% samples. At 3 at-% Fe, corresponding impurity ions induce surface energy changes that have a substantial impact on particle shape. With regard to the functional properties associated with transition metal ions in insulating MgO host lattices, the here presented insights underline that annealing-induced reorganization of oxide nanoparticles provides important parameters to control distribution and localization of impurity ions.