Reversed ageing of Fe3_3O4_4 nanoparticles by hydrogen plasma

Magnetite (Fe3O4) nanoparticles suffer from severe ageing effects when exposed to air even when they are dispersed in a solvent limiting their applications. In this work, we show that this ageing can be fully reversed by a hydrogen plasma treatment. By x-ray absorption spectroscopy and its associated magnetic circular dichroism, the electronic structure and magnetic properties were studied before and after the plasma treatment and compared to results of freshly prepared magnetite nanoparticles. While aged magnetite nanoparticles exhibit a more γ-Fe2O3 like behaviour, the hydrogen plasma yields pure Fe3O4 nanoparticles. Monitoring the temperature dependence of the intra-atomic spin dipole contribution to the dichroic spectra gives evidence that the structural, electronic and magnetic properties of plasma treated magnetite nanoparticles can outperform the ones of the freshly prepared batch

Розвиток суспільно-політичного процесу на Волині в період незалежності

У статті розглянуто основні етапи розвитку суспільно-політичного процесу на Волині в період незалежності України. Трансформаційні процеси, що проходять в області, попри свою місцеву особливість, виходять із чергового етапу розвитку політичної системи України, а отже, розвиток суспільно-політичного процесу на Волині прямо залежний від всеукраїнського процесу трансформації.In the article the basic stages of the development of social and political process are considered in Volyn region during the period of independence of Ukraine. The transformation processes, which pass in this region, without regard to the local feature go out from the regular stage of the development of the political system of Ukraine, and consequently, the development of social and political process in Volyn region depend directly upon the all-Ukrainian process of transformation

Intramolecular crossover from unconventional diamagnetism to paramagnetism of palladium ions probed by soft X-ray magnetic circular dichroism

The case of palladium(II) ions in molecular polyoxopalladates highlights the importance of accounting not only for nearest neighbour atoms or ions in order to understand, model or predict magnetic characteristics. Here, using site-specific soft X-ray magnetic circular dichroism (XMCD), the effects of different bond lengths, delocalization of 4d electrons, and 4d spin-orbit coupling on the electronic and magnetic properties are investigated and three different states identified: Conventional diamagnetism in a square-planar O4 coordination environment, paramagnetism caused by four additional out-of-plane oxygen anions, and an unusual diamagnetic state in the diamagnetic/paramagnetic crossover region modified by significant mixing of states and facilitated by the substantial 4d spin-orbit coupling. The two diamagnetic states can be distinguished by characteristic XMCD fine structures, thereby overcoming the common limitation of XMCD to ferro-/ferrimagnetic and paramagnetic materials in external magnetic fields. The qualitative interpretation of the results is corroborated by simulations based on charge transfer multiplet calculations and density functional theory results

XMCD on Fe-based nanoparticles: Two examples of theory and experiment complementing one another

Two examples of recent research are presented that emphasise the importance of combining experimental approaches in x-ray absorption spectroscopy and its associated magnetic circular dichroism with density functional theory to gain a more fundamental understanding. In particular we show how to tailor the magnetic properties of FePt nanoparticles by choosing an appropriate capping material and how the frequently neglected and unpleasant intra-atomic dipole term can be used to monitor a phase transition in magnetite nanoparticles that cannot be revealed with commonly used methods for the corresponding bulk material

Rietveld structure refinement to optimize the correlation between cation disordering and magnetic features of CoFe2_2O4_4 nanoparticles

The structural properties of cobalt ferrite nanoparticles have significant effects on their magnetic behavior. In the current study, we thoroughly scrutinized and optimized the structural characteristics of CoFe$_2$O$_4$ nanoparticles and the correlation with their magnetic properties as a function of the synthesis parameters using Rietveld structure refinement. Nanoparticles were synthesized using co-precipitation method based on design of experiments and then characterized using X-ray diffraction, vibrating sample magnetometry, transmission electron microscopy, and energy dispersive X-ray spectroscopy analyses.Based on response surface methodology studies, we identified factors that had an effect on the structural and magnetic features. In order to reach maximum magnetization, the cations distribution was optimized, and the pH amount and reaction temperature were identified as the most influential factors.We observed that the initial cation ratio of Co$^{2+}$/Fe$^{3+}$ sharply affected the cations distribution, which was subsequently involved in the different structural characteristics and magnetization of nanoparticles. Thiscan be attributed to the hybrid structure formation and magnetic exchange interactions of cations. Finally, the maximum magnetization was achieved at the optimum cations distribution of (Co$_{0.32}$Fe$_{0.68}$)(Co$_{0.70}$Fe$_{1.30}$)O$_4$, where the difference between distributed cobalt cations in tetrahedral and octahedral sites was minimum

Statistical approach of synthesize CoFe 2 O 4 nanoparticles to optimize their characteristics using response surface methodology

The performance of magnetic nanoparticles in different applications is severely depended on their size characteristics, so the study of effective parameters on these properties can play significant roles in qualifications of nanoparticles. In present work, some important factors on size features of CoFe2O4 superparamagnetic nanoparticles include the mixing order of synthesis components, the utilized reduction agents, stabilization process, and chelating mechanisms were investigated. Moreover, in order to optimize several influential factors such as the temperature, pH, and cation ratio of reaction, the experimental design was done by using central composite design method of response surface methodology. The simultaneous effects on the particles size and their size distribution were investigated by different methods i.e. dynamic light scattering, X-ray diffraction, Fourier transform inferred spectroscopy, vibration sample magnetometer, and transmission electron microscopy. Results demonstrated the mixing order of reduction agent to salt solution and also the employing of NH4OH as a reduction agent could cause to significant decreasing of particles size and size distribution. Furthermore, the nitric acid could stabilize and chelate nanoparticles more appropriate than citric acid. Based on the optimization results, the quadratic polynomial models were fitted on the responses which could predict their amounts, while temperature, pH, and their interactions had higher effectiveness. In addition, the optimum amounts of particle size (14 nm) and size distribution (4.61 nm) were achieved while temperature, pH, and cation ratio amounts are equal to 89.82 °C, 11, and 0.52, respectivel

How the surface affects the electronic and magnetic properties of magnetite nanoparticles

Magnetite (Fe3O4) nanoparticles are objects of intense research activities due to their broad range of applications covering technological, medical, and environmental applications. They are used e.g. for rotary shaft sealing, oscillation damping, position sensing, magnetic inks for jet printing, as contrast agents in magnetic resonance imaging, and to remove heavy metals from wastewater. In addition, magnetite is a half-metal with a predicted negative spin polarisation making magnetite interesting for spintronics. For all applications, a high quality of magnetite is crucial to obtain the desired properties. In this work, we studied the influence of the surface on the electronic and magnetic properties of magnetite nanoparticles by means of x-ray absorption near-edge spectroscopy (XANES) and its associated magnetic circular dichroism (XMCD). In particular, we investigated ensembles of magnetite nanoparticles with a mean diameter of 3nm, 6nm or 9nm and the influence of capping the particles with a 3nm thick silica shell or organic ligands. XANES and XMCD gives the unique possibility to distinguish between the three different Fe species in magnetite, i.e. tetrahedrally coordinated Fe3+ ions, octahedrally coordinated Fe3+, and octahedrally coordinated Fe2+, by using different photon energies for hysteresis measurements. Besides changes in the electronic structure, i.e. in the density of unoccupied 3d states monitored by XANES, and the effective spin magnetic moments, we obtained a different spin canting behaviour of Fe ions in magnetite at different lattice sites from the magnetic field dependent XMCD as shown in the figure below. The results are discussed regarding different exchange mechanisms and possible advantages and drawbacks for applications. Measurements were performed at beamline UE46-PGM1, HZB – BESSY II synchrotron radiation facility. We thank the BESSY II staff for kind support during beamtimes. Financially supported by BMBF (05 ES3XBA/5) and DFG (WE2623/3-1)

Magnetic-Plasmonic Heterodimer Nanoparticles: Designing Contemporarily Features for Emerging Biomedical Diagnosis and Treatments

Magnetic-plasmonic heterodimer nanostructures synergistically present excellent magnetic and plasmonic characteristics in a unique platform as a multipurpose medium for recently invented biomedical applications, such as magnetic hyperthermia, photothermal therapy, drug delivery, bioimaging, and biosensing. In this review, we briefly outline the less-known aspects of heterodimers, including electronic composition, interfacial morphology, critical properties, and present concrete examples of recent progress in synthesis and applications. With a focus on emerging features and performance of heterodimers in biomedical applications, this review provides a comprehensive perspective of novel achievements and suggests a fruitful framework for future research