Search results for "Paramagnetism"
showing 10 items of 354 documents
Unexpected magnetism in nanomaterials
2013
Conventional magnetic order in a material requires the partially filled d or f bands. The exchange interactions between the electrons in these partially filled bands give rise to a magnetic order. However, the discovery of unexpected magnetism observed in some nanomaterials, which have the d and f shells either completely empty or full, has challenged our understanding of magnetism in conventional materials. The magnetism in nanomaterials shows the effects of reduced dimensions, reduced coordination of atoms at the surface and some quantum effects which dominate at low dimensions. In this review paper we give a brief review and discuss the unexpected magnetism experimentally observed and/or…
Dynamics of the incorporation of Co into the wurtzite ZnO matrix and its magnetic properties
2015
Made available in DSpace on 2022-04-29T07:25:55Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-07-25 Financiadora de Estudos e Projetos Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Abstract Bulk Co-doped ZnO (Zn1-xCoxO) samples were prepared and studied with particular emphasis on their compositions, structures, and magnetic properties. A detailed microstructural analysis was conducted to investigate the nature of Co incorporation into the wurtzite ZnO matrix. The Zn1-xCoxO ceramic samples were prepared using the standard solid-state reaction method with different Co molar concentrations of u…
Effect of precursor concentration on size evolution of iron oxide nanoparticles
2017
Thermal decomposition is a promising route for the synthesis of magnetic nanoparticles. The simplicity of the synthesis method is counterbalanced by the complex chemistry of the system such as precursor decomposition and surfactant–reducing agent interactions. Control over nanoparticle size is achieved by adjusting the reaction parameters, namely, the precursor concentration. The results, however, are conflicting as both an increase and a decrease in nanoparticle size, as a function of increasing concentration, have been reported. Here, we address the issue of size-controlled synthesis via the precursor concentration. We synthesized iron oxide nanoparticles with sizes from 6 nm to 24 nm wit…
Electroswitching of the single-molecule magnet behaviour in an octahedral spin crossover cobalt(ii) complex with a redox-active pyridinediimine ligand
2020
Thermal-assisted spin crossover and field-induced slow magnetic relaxation coexist in the solid state for the mononuclear cobalt(II) complex with the non-innocent 2,6-bis(N-4-methoxyphenylformimidoyl)pyridine ligand. One-electron oxidation of the paramagnetic low-spin CoII ion (SCo = 1/2) to the diamagnetic low-spin CoIII ion (SCo = 0) leads to the electroswitching of the slow magnetic relaxation in acetonitrile solution.
Gold Nanowired: A Linear (Au25)n Polymer from Au25 Molecular Clusters
2014
Au25(SR)18 has provided fundamental insights into the properties of clusters protected by monolayers of thiolated ligands (SR). Because of its ultrasmall core, 1 nm, Au25(SR)18 displays molecular behavior. We prepared a Au25 cluster capped by n-butanethiolates (SBu), obtained its structure by single-crystal X-ray crystallography, and studied its properties both experimentally and theoretically. Whereas in solution Au25(SBu)18(0) is a paramagnetic molecule, in the crystal it becomes a linear polymer of Au25 clusters connected via single Au-Au bonds and stabilized by proper orientation of clusters and interdigitation of ligands. At low temperature, [Au25(SBu)18(0)]n has a nonmagnetic ground s…
Magnetic Langmuir–Blodgett films of ferritin with different iron loadings
2005
Abstract Magnetic Langmuir–Blodgett multilayers of two ferritin molecules 1 and 2 , containing, respectively, 4220 and 3062 Fe atoms have been prepared by using the adsorption properties of a 6/1 mixed monolayer of dioctadecyldimethylammonium bromide (DODABr) and methyl stearate (SME). Transfer ratios close to unity were reached giving rise to LB films with a strong red colour. Infrared and UV–vis spectroscopy indicates that ferritin molecules are incorporated within the LB films. Magnetic measurements show that the superparamagnetic properties of these molecules are preserved. Thus, a marked hysteresis loop of magnetisation is obtained for LB films of 1 and 2 with a coercive field of 3400 …
Distinct hematite populations from simultaneous fitting of Mössbauer spectra from Meridiani Planum, Mars
2010
[1] At Meridiani Planum, Mars, hematite occurs as a lag of ∼5 mm diameter spherules and their fragments and within the matrix of the sulfate-rich outcrop as <30 μm particles. Well crystalline and chemically pure bulk hematite undergoes a magnetic transition at ∼264 K (Morin transition) that can be detected by Mossbauer spectroscopy and is within the Martian diurnal temperature range. We analyzed outcrop and lag hematite Mossbauer spectra obtained by the Mars Exploration Rover (MER) Opportunity as a function of temperature using a simultaneous fitting procedure to determine the Morin temperature and the temperature interval over which it occurs. Mossbauer spectra for terrestrial hematite-bea…
Structural and Magnetic Insights into the Trinuclear Ferrocenophane and Unexpected Hydrido Inverse Crown Products of Alkali‐Metal‐Mediated Manganatio…
2008
With the aim of introducing the diisopropylamide [NiPr(2)](-) ligand to alkali-metal-mediated manganation (AMMMn) chemistry, the temperature-dependent reactions of a 1:1:3 mixture of butylsodium, bis(trimethylsilylmethyl)manganese(II), and diisopropylamine with ferrocene in hexane/toluene have been investigated. Performed at reflux temperature, the reaction affords the surprising, ferrocene-free, hydrido product [Na(2)Mn(2) (mu-H)(2){N(iPr)(2)}(4)]2 toluene (1), the first Mn hydrido inverse crown complex. Repeating the reaction rationally, excluding ferrocene, produces 1 in an isolated crystalline yield of 62 %. At lower temperatures, the same bimetallic amide mixture leads to the manganati…
Ellipsoid-shaped superparamagnetic nanoclusters through emulsion electrospinning.
2015
Ellipsoid-shaped nanoclusters composed of single superparamagnetic nanoparticles can be generated by emulsion electrospinning. Stretching and subsequent solvent evaporation of iron oxide loaded emulsion droplets during the emulsion electrospinning process enables the creation of such structures embedded in polymer nanofibers. Dissolution of the polymer fibers yields an aqueous dispersion of the inorganic clusters which are the first example of ellipsoid-shaped superparamagnetic nanoclusters with a high saturation magnetization (∼47 emu g(-1)).
Insertion of a single-molecule magnet inside a ferromagnetic lattice based on a 3D bimetallic oxalate network: Towards molecular analogues of permane…
2014
The insertion of the single-molecule magnet (SMM) [MnIII(salen) (H2O)]2 2+ (salen2-=N,N-ethylenebis- (salicylideneiminate)) into a ferromagnetic bimetallic oxalate network affords the hybrid compound [MnIII(salen)(H2O)] 2[MnIICrIII(ox)3] 2×(CH3OH)×(CH3CN)2 (1). This cationic Mn2 cluster templates the growth of crystals formed by an unusual achiral 3D oxalate network. The magnetic properties of this hybrid magnet are compared with those of the analogous compounds [Mn III(salen)(H2O)]2[ZnIICr III(ox)3]2×(CH3OH) ×(CH3CN)2 (2) and [InIII(sal 2-trien)][MnIICrIII(ox)3] ×(H2O)0.25×(CH3OH) 0.25×(CH3CN)0.25 (3), which are used as reference compounds. In 2 it has been shown that the magnetic isolatio…