1,720,981 research outputs found
Tuning the superparamagnetic effect in ZnFe2O4 nanoparticles with Mg, Ga doping
No full textZnFe2O4 nanoparticles are an amazing class of materials whose magnetic features are particularly appealing for the biomedical field. Their key property is the superparamagnetic behaviour at room temperature, strictly dependent on particle sizes values and cation distribution on the spinel sites, easily tuneable by substitution of dopants and by proper synthesis methods. In this paper, we focused on the undoped and Mg (on Zn site) and/or Ga (on Fe site) substituted ferrites synthesized by co-precipitation route. XRPD, SEM and Micro-Raman techniques allowed us to ensure the good quality of the samples, to determine the dopants location into spinel lattice and to estimate an average crystallite size of about 5 nm. A superparamagnetic behaviour with maxima magnetization values at room temperature between 4 and 7 emu/g at the highest applied magnetic field of 1T was disclosed, as well as a clear dependence of the blocking temperature on the cationic disorder within the two sublattices, which strengthens the magnetic interactions thus moving the transition to an ordered blocked state at higher temperatures. The electron paramagnetic resonance inspection confirmed the superparamagnetic behavior, excluding extrinsic contribution from iron oxides phases, so demonstrating that the magnetic properties depend on the inversion degree, related to the structural disorder, of the spinel phase
Magnetic order in TM-doped TiO2 single crystals
No full textNeedle shaped single crystals of TM-doped rutile TiO2 (TM=Cr, Mn, Fe, Co, Ni, Cu), grown in a sodium tetraborate melt with the flux method, are analysed in their structural and optical properties with a multitechnique approach. The ferromagnetic behaviour, observed up to room temperature, overlapping the prevailing expected paramagnetism, is investigated by means of static magnetization measurements performed at different temperatures and magnetic fields. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Effects of reaction atmosphere on physico-chemical properties of V-doped FeNb11O29
No full textFeNb11O29, pure or doped with metal transition ions, is a very promising material with advanced multifunctionalities
and interesting applicative perspectives. It is isostructural with Nb12O29, one of the rare compounds
in which Nb displays a local magnetic moment and shows both antiferromagnetic ordering and metallic
conductivity at low temperatures. In this work we have synthesized and studied Fe0.8V0.2Nb11O29 monoclinic
powders. In particular we monitored the effects on structural, electronic and magnetic properties in samples
produced in different atmospheres to stabilize cations with different oxidation states.
We have demonstrated that the reaction atmosphere influences the phase homogeneity, the crystallite size
and the amount of paramagnetic centres, with a transformation of Fe3+ in Fe2+ when an inert atmosphere is
used, as proved by the absence, in this case, of any electron paramagnetic resonance signal. Also the Raman
spectra result to be affected due to the change of coordination polyhedra. Subsequent re-oxidation of reduced
powders brings to the monophasic iron niobate again containing Fe3+ demonstrating the reversibility of redox
process. This reversibility is accompanied by a complete restoring of monoclinic structure evidenced by X-ray
diffraction data and by Raman measurements, which allowed also to follow in situ the spectral changes induced
by laser heating
Role of non-magnetic dopants (Ca, Mg) in GdFeO3 perovskite nanoparticles obtained by different synthetic methods: structural, morphological and magnetic properties
No full textGdFeO3 perovskite attracted large interest in different fields thanks to peculiar magnetic and optical properties that are further tunable by means of doping processes and achievable on both Gd and Fe sites or by properly choosing the synthesis routes. In this paper, nanometric GdFeO3 compounds, undoped and doped with diamagnetic Ca2+ and Mg2+ ions, were synthesized by microwave assisted, sol–gel, and polyol syntheses and characterized by X-ray diffraction, showing solid solutions formation. Raman spectroscopy allowed us to confirm, from peak enlargements, the Ca and Mg substitution on Gd and Fe sites, respectively. The magnetic data showed the presence of magnetic domains as consequence of doping with diamagnetic ions, which seem to play a crucial role in the magnetic activity of the compounds. A superparamagnetic behaviour is evidenced; nevertheless, its intrinsic character is not definitely demonstrated. Indeed, the possible presence of traces of magnetic impurities, which are easily obtainable in these samples, such as iron oxides, must be taken into account
Band offset and gap tuning of tetragonal CuO-SrTiO3 heterojunctions
No full textIn this work we analyze the electronic structure at the junction between a SrTiO3 (001) single crystal and a thin tetragonal CuO layer, grown by off-axis rf sputtering. A detailed characterization of the film growth, based on atomic force microscopy and x-ray photoelectron diffraction measurements, demonstrates the epitaxial growth. We report several markers of a thickness-dependent modification of the film gap, found on both Cu2p and valence band spectra; through spectroscopic ellipsometry analysis, we provide direct proof of a band gap increase in the tetragonal CuO layer (1.57 eV) with respect to the thicker monoclinic CuO layer (1.35 eV). This phenomenon is further discussed in light of cluster calculations and density functional theory +U simulations. Finally, we report the full experimental band junction diagram, showing a staggered configuration suitable for charge-separation applications, such as photovoltaics and photocatalysis; this configuration is observed up to very low (<3 nm) film thickness due to the gap broadening effect
Publisher Correction: Fe-functionalized paramagnetic sporopollenin from pollen grains: one-pot synthesis using ionic liquids (Scientific Reports, (2020), 10, 1, (12005), 10.1038/s41598-020-68875-6)
No full textIn the original version of this Article, F. Rossella was incorrectly listed as a corresponding author. The correct corresponding author for this Article is C.S. Pomelli. Correspondence and request for materials should be addressed to [email protected]. This error has now been corrected in the HTML and PDF versions of the Article
Ferromagnetic and ordered MnSi(111) epitaxial layers
No full textWe report a comprehensive study of ordered MnSi films grown on Si (111) which provides clear proofs that these MnSi films have the same magnetic and electronic properties of bulk MnSi compound, so closing a long-standing question. Furthermore, our measurements show the presence of a room-temperature ferromagnetic transition consistent with the ferromagnetic ground state predicted for Mn atoms with reduced coordination near surfaces and interfaces of silicon by recent calculations of Hortamani et al. [Phys. Rev. B 78, 104402 (2008)]. The possibility of growing layers on semiconductors which are ferromagnetic at room temperature RT is of paramount importance for nonvolatile memories and spintronic devices based on the injection of spin-polarized current from a ferromagnetic metal into a semiconductor. In this perspective MnSi films grown on Si substrates represent an interesting case study
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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