Hydrothermal synthesis of Fe and Mn doped SnO2 and its magnetic structures

The dilute magnetic semiconductor of Sn1-x-yMnxFeyO2 (0 <= x <= 0.10, 0 <= y <= 0.10) Were syhthesized with the hydrothermal method using SnCl4, Mn(CH3COO)(2) center dot 4H(2)O and FeCl3 center dot 6H(2)O as the raw materials. The structure, morphologies and magnetic properties of the sample were characterized via X-ray powder diffractometer(XRD), transmission electron microscopy(TEM), Raman spectrum and superconducting and quantum interference device(SQUIT), and Mossbeaur spectrum. No secondary phase was found in the XRD spectrum. The morphology of the samples is affected by the kind or the mount of transition metal. The local vibrating model-of Mn Positioned SnO2 sites was found in Raman spectrum. The measured magnetic results indicate that when x = 0.10, y = 0, the sample exhibits strong magnetization in low-temperature (5 K), but the magnetization decrease rapidly at room. temperature; In contrast, when x = 0, y = 0.1, the sample's magnetization and coercivity are both small, but being temperature independent. Mossbeaur spectra indicates that part of the Fe is ferromagnetic coupled, and the simulating results indicate that the ferromagnetic character is intrinsic.

Probing the ultimate limits of plasmonic enhancement.

Metals support surface plasmons at optical wavelengths and have the ability to localize light to subwavelength regions. The field enhancements that occur in these regions set the ultimate limitations on a wide range of nonlinear and quantum optical phenomena. We found that the dominant limiting factor is not the resistive loss of the metal, but rather the intrinsic nonlocality of its dielectric response. A semiclassical model of the electronic response of a metal places strict bounds on the ultimate field enhancement. To demonstrate the accuracy of this model, we studied optical scattering from gold nanoparticles spaced a few angstroms from a gold film. The bounds derived from the models and experiments impose limitations on all nanophotonic systems.

Dissipative Optomechanics in a Michelson--Sagnac Interferometer

Dissipative optomechanics studies the coupling of the motion of an optical element to the decay rate of a cavity. We propose and theoretically explore a realization of this system in the optical domain, using a combined Michelson-Sagnac interferometer, which enables a strong and tunable dissipative coupling. Quantum interference in such a setup results in the suppression of the lower motional sideband, leading to strongly enhanced cooling in the non-sideband-resolved regime. With state-of-the-art parameters, ground-state cooling and low-power quantum-limited position transduction are both possible. The possibility of a strong, tunable dissipative coupling opens up a new route towards observation of such fundamental optomechanical effects as nonlinear dynamics. Beyond optomechanics, the suggested method can be readily transferred to other setups involving nonlinear media, atomic ensembles, or single atoms.

Magnetic properties of copper hexadecaphthalocyanine (F16CuPc) thin films and powders

The structural and magnetic properties of F16CuPc thin films and powder, including x-ray diffraction (XRD), superconducting quantum interference device (SQUID) magnetometry, and theoretical modelling of exchange interactions are reported. Analysis of XRD from films, with thickness ranging between 100 and 160 nm, deposited onto Kapton and a perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride (PTCDA) interlayer shows that the stacking angle (defined in the text) of the film is independent of the thickness, but that the texture is modified by both film thickness and substrate chemistry. The SQUID measurements suggest that all samples are paramagnetic, a result that is confirmed by our theoretical modelling including density functional theory calculations of one-dimensional molecular chains and Green's function perturbation theory calculations for a molecular dimer. By investigating theoretically a range of different geometries, we predict that the maximum possible exchange interaction between F16CuPc molecules is twice as large as that in unfluorinated copper-phthalocyanine (CuPc). This difference arises from the smaller intermolecular spacing in F16CuPc. Our density functional theory calculation for isolated F16CuPc molecule also shows that the energy levels of Kohn-Sham orbitals are rigidly shifted similar to 1 eV lower in F16CuPc compared to CuPc without a significant modification of the intramolecular spin physics, and that therefore the two molecules provide a suitable platform for independently varying magnetism and charge transport. 

Magnetic properties of TlCu2-xFexSe2 crystals

The magnetic properties of two compositions of random solutions in the TlCu2-xFexSe2 system with x = 0.2 and 0.45 have been investigated by superconducting quantum interference device magnetometry. The crystal structure is of a layer type and ordering due to the iron atoms occurs at low temperatures, with T-c = 85 K for x = 0.2 and T-c = 130 K for x = 0.45. The samples were highly textured crystals and the magnetic moments of both compositions were found to align along the c axis of the structure. The saturation moments were found to be 1.5 mu(B)/Fe x = 0.2 and 0.66 mu(B)/Fe for x = 0.45. (c) 2005 American Institute of Physics.

Crystal and magnetic structure of Mn3IrSi

A new ternary Ir-Mn-Si phase with stoichiometry Mn₃IrSi has been synthesized and found to crystallize in the cubic AlAu₄-type structure, space group P2₁3 with Z=4, which is an ordered form of the beta-Mn structure. The unit cell dimension was determined by x-ray powder diffraction to a=6.4973(3) Angstrom. In addition to the crystal structure, we have determined the magnetic structure and properties using superconducting quantum interference device magnetometry and Rietveld refinements of neutron powder diffraction data. A complex noncollinear magnetic structure is found, with magnetic moments of 2.97(4)u(B) at 10 K only on the Mn atoms. The crystal structure consists of a triangular network built up by Mn atoms, on which the moments are rotated 120degrees around the triangle axes. The magnetic unit cell is the same as the crystallographic and carries no net magnetic moment. The Neel temperature was determined to be 210 K. A first-principles study, based on density functional theory in a general noncollinear formulation, reproduces the experimental results with good agreement. The observed magnetic structure is argued to be the result of frustration of antiferromagnetic couplings by the triangular geometry.

Evaluation of La1−xSrxMnO3 (0 ≤ x < 0.4) synthesised via a modified sol–gel method as mediators for magnetic fluid hyperthermia

A range of lanthanum strontium manganates (La1−xSrxMnO3–LSMO) where 0 ≤ x < 0.4 were prepared using a modified peroxide sol–gel synthesis method. The magnetic nanoparticle (MNP) clusters obtained for each of the materials were characterised using scanning electron microscopy (SEM), X-ray powder diffraction (XRD) and infra-red (IR) spectroscopy in order to confirm the crystalline phases, crystallite size and cluster morphology. The magnetic properties of the materials were assessed using the Superconducting quantum interference device (SQUID) to evaluate the magnetic susceptibility, Curie temperature (Tc) and static hysteretic losses. Induction heating experiments also provided an insight into the magnetocaloric effect for each material. The specific absorption rate (SAR) of the materials was evaluated experimentally and via numerical simulations. The magnetic properties and heating data were linked with the crystalline structure to make predictions with respect to the best LSMO composition for mild hyperthermia (41 °C ≤ T ≤ 46 °C). La0.65Sr0.35MnO3, with crystallite diameter of 82.4 nm, (agglomerate size of ∼10 μm), Tc of 89 °C and SAR of 56 W gMn−1 at a concentration 10 mg mL−1 gave the optimal induction heating results (Tmax of 46.7 °C) and was therefore deemed as most suitable for the purposes of mild hyperthermia, vide infra.

Synthesis of Bio-Compatible SPION–based Aqueous Ferrofluids and Evaluation of RadioFrequency Power Loss for Magnetic Hyperthermia

Bio-compatible magnetic fluids having high saturation magnetization find immense applications in various biomedical fields. Aqueous ferrofluids of superparamagnetic iron oxide nanoparticles with narrow size distribution, high shelf life and good stability is realized by controlled chemical co-precipitation process. The crystal structure is verified by X-ray diffraction technique. Particle sizes are evaluated by employing Transmission electron microscopy. Room temperature and low-temperature magnetic measurements were carried out with Superconducting Quantum Interference Device. The fluid exhibits good magnetic response even at very high dilution (6.28 mg/cc). This is an advantage for biomedical applications, since only a small amount of iron is to be metabolised by body organs. Magnetic field induced transmission measurements carried out at photon energy of diode laser (670 nm) exhibited excellent linear dichroism. Based on the structural and magnetic measurements, the power loss for the magnetic nanoparticles under study is evaluated over a range of radiofrequencies.

Magnetism of isolated Mn12 single-molecule magnets detected by magnetic circular dichroism: Observation of spin tunneling with a magneto-optical technique

We report magnetic and magneto-optical measurements of two Mn12 single-molecule magnet derivatives isolated in organic glasses. Field-dependent magnetic circular dichroism (MCD) intensity curves (hysteresis cycles) are found to be essentially identical to superconducting quantum interference device magnetization results and provide experimental evidence for the potential of the optical technique for magnetic characterization. Optical observation of magnetic tunneling has been achieved by studying the decay of the MCD signal at weak applied magnetic field

Synthesis of High Coercivity Cobalt Nanotubes with Acetate Precursors and Elucidation of the Mechanism of Growth

Cobalt nanotubes (CoNTs) with very high longitudinal coercivity were prepared by electrodeposition of cobalt acetate for the first time by using anodized alumina (AAO) template. They were then characterized with X-ray diffraction (XRD), a field emission scanning electron microscope (FESEM), and a transmission electron microscope (TEM). Formation of a highly ordered hexagonal cobalt phase is observed. Room temperature SQUID (superconducting quantum interference device) magnetometer measurements indicate that the easy axis of magnetization is parallel to the nanotube axis. These CoNTs exhibit very high longitudinal coercivity of ∼820 Oe. A very high intertubular interaction resulting from magnetostatic dipolar interaction between nanotubes is observed. Thick-walled nanotubes were also fabricated by using cobalt acetate tetrahydrate precursors. A plausible mechanism for the formation of CoNTs based on mobility assisted growth is proposed. The role of the hydration layer and the mobility of metal ions are elucidated in the case of the growth mechanism of one-dimensional geometry

Syntheses, spectroelectrochemical studies, and molecular and electronic structures of ferrocenyl ene-diynes

The readily available complex 1,1-dibromo-2-ferrocenylethylene provides a convenient entry point for the preparation of a wide range of cross-conjugated 1,1-bis(alkynyl)-2-ferrocenylethenes through simple Pd(0)/Cu(I)-mediated cross-coupling reactions with 1-alkynes. The ferrocene moiety in compounds of the general form FcCHC(CCR)2 is essentially electronically isolated from the cross-conjugated π system, as evidenced by IR and UV−vis spectroelectrochemical experiments and quantum chemical calculations. In contrast to the other examples which give stable ferrocenium derivatives upon electrochemical oxidation, the aniline derivatives [FcCHC(CCC6H4NH2-4)2]+ and [FcCHC(CCC6H4NMe2-4)2]+ proved to be unstable on the time scale of the spectroelectrochemical experiments, leading to passivation of the electrode surface over time. There is no significant thermodynamic stabilization of the radical anion [FcCHC(CCC6H4NO2-4)2]− relative to the neutral and dianionic analogues, although the dianion [FcCHC(CCC6H4NO2- 4)2]2− could be studied as a relatively chemically stable species and is well described in terms of two linked nitrophenyl radicals. The capacity to introduce a relatively isolated point charge at the periphery of the cross-conjugated π system appears to make these complexes useful templates for the construction of electrochemically gated quantum interference transistors.

Mapping the Intramolecular Vibrational Energy Flow in Proteins Reveals Functionally Important Residues

Unveiling the mechanisms of energy relaxation in biomolecules is key to our understanding of protein stability, allostery, intramolecular signaling, and long-lasting quantum coherence phenomena at ambient temperatures. Yet, the relationship between the pathways of energy transfer and the functional role of the residues involved remains largely unknown. Here, we develop a simulation method of mapping out residues that are highly efficient in relaxing an initially localized excess vibrational energy and perform site-directed mutagenesis functional assays to assess the relevance of these residues to protein function. We use the ligand binding domains of thyroid hormone receptor (TR) subtypes as a test case and find that conserved arginines, which are critical to TR transactivation function, are the most effective heat diffusers across the protein structure. These results suggest a hitherto unsuspected connection between a residue`s ability to mediate intramolecular vibrational energy redistribution and its functional relevance.

Attachment of magnetic molecules on a nanoSQUID

A novel procedure combining monolayer self-assembly with electron beam lithography has been developed for attaching ferritin nanoparticles to a submicron thin-film SQUID (superconducting quantum interference device). After opening a window in the PMMA (polymethylmethacrylate) resist, organic linker molecules are used to attach ferritin to the exposed parts of the gold overlayer of a Nb nanoSQUID. This allows the magnetic nanoparticles to be located optimally as far as magnetic coupling to the nanoSQUID is concerned.

Biomagnetic Methods: Technologies Applied to Pharmaceutical Research

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Tunelamento quântico molecular: efeito de acoplamentos no malonaldeído

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)