Search results for "Magnetism"
showing 10 items of 1934 documents
Probing the Size Effect of Co2FeGa-SiO2@C Nanocomposite Particles Prepared by a Chemical Approach
2010
In this contribution, we report the chemical synthesis of carbon coated, silica supported Co2FeGa (Co2FeGa-SiO2@C) nanocomposite particles. The particle size of Co2FeGa particles can be tuned by varying the amount of silica supports. The dependences of the crystal structure and magnetic properties on particle size have been investigated by synchrotron radiation based X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) spectroscopy, transmission electron microscope (TEM), 57Fe Mossbauer spectroscopy, and superconducting quantum interference device (SQUID). The superparamagnetic critical size of Co2FeGa Heusler nanoparticles is found to be ∼17 nm by correlating the TEM derived par…
Synthesis, characterization and functionalization of nearly mono-disperse copper ferrite CuxFe3−xO4 nanoparticles
2011
Magnetic nanocrystals are of great interest for a fundamental understanding of nanomagnetism and for their technological applications. CuxFe3−xO4 nanocrystals (x ≈ 0.32) with sizes ranging between 5 and 7 nm were synthesized starting from Cu(HCOO)2 and Fe(CO)5 using oleic acid and oleylamine as surfactants. The nanocrystals were characterized by high-resolution transmission electron microscopy (HRTEM), electron diffraction (ED), magnetization studies and Mossbauer spectroscopy. The CuxFe3−xO4 particles are superparamagnetic at room temperature 300 K with a saturation magnetization of 30.5 emu g−1. Below their blocking temperature of 60 K, they become ferrimagnetic, and at 5 K they show a co…
Manganese iron oxide superparamagnetic powder by mechanochemical processing. Nanoparticles functionalization and dispersion in a nanofluid
2012
Manganese ferrite nanoparticles were synthesized using a High-Energy Ball-Milling mechanochemical method. After 1 h of milling, the process produces a material consisting of single crystalline domain nanoparticles having a diameter of about 8 nm. Chemical properties of the synthesized powders allow an easy functionalization with citric acid. Both as-obtained and functionalized samples show superparamagnetic behaviour at room temperature, and the functionalized powder is stably dispersible in aqueous media at physiological pH. The average hydrodynamic diameter is equal to similar to 60 nm. Nanoparticles obtained by the reported High-Energy Ball-Milling method can be synthesized with high yie…
Domain wall transformations and hopping in La0.7Sr0.3MnO3nanostructures imaged with high resolution x-ray magnetic microscopy
2014
We investigate the effect of electric current pulse injection on domain walls in La(0.7)Sr(0.3)MnO(3) (LSMO) half-ring nanostructures by high resolution x-ray magnetic microscopy at room temperature. Due to the easily accessible Curie temperature of LSMO, we can employ reasonable current densities to induce the Joule heating necessary to observe effects such as hopping of the domain walls between different pinning sites and nucleation/annihilation events. Such effects are the dominant features close to the Curie temperature, while spin torque is found to play a small role close to room temperature. We are also able to observe thermally activated domain wall transformations and we find that,…
Dynamics of paramagnetic nanostructured rods under rotating field
2011
International audience; The dynamical rotational behavior of magnetic nanostructured rods based on the auto-association of maghemite nanoparticles and block-copolymers is probed by optical microscopy under rotating fields i n a s imple l iquid. The reorientation of the rods by a field rotated by 90° is first studied. The measured relaxation is characteristic of param-agnetic objects. Under a stationnary rotating field, a synchronous rotational regime is observed at low field frequency. Above a frequency threshold which scales as H^2 , the dynamics becomes asynchronous with back-and-forth rotations. These behaviors are well predicted by the presented model.
ELECTRICAL-FIELD CONTROL OF MAGNETISM MEDIATED BY STRAIN IN Ni NANOSTRUCTURES FABRICATED ON PRE-POLED PMN–PT (011)
2013
We investigate the effects of piezoelectric-generated strain on the magnetization configuration of Ni nanostructures fabricated on pre-poled piezoelectric (011) [ Pb ( Mg 0.33 Nb 0.66) O 3]0.68–[ PbTiO 3]0.32 (PMN–PT) by high resolution X-ray microscopy. We observe a strong uniaxial anisotropy in the Ni nanostructures, due to the relaxation of the substrate following the deposition of the Ni . The anisotropy can be modified by the application of an electric field to the piezoelectric substrate (thus generating a piezoelectric strain in the system) through the magneto-elastic effect. By applying an electric field to the PMN–PT, the magnetization configuration in nanostructured Ni squares an…
Ultrafast antiferromagnetic switching in NiO induced by spin transfer torques
2020
NiO is a prototypical antiferromagnet with a characteristic resonance frequency in the THz range. From atomistic spin dynamics simulations that take into account the crystallographic structure of NiO, and in particular a magnetic anisotropy respecting its symmetry, we describe antiferromagnetic switching at THz frequency by a spin transfer torque mechanism. Sub-picosecond S-state switching between the six allowed stable spin directions is found for reasonably achievable spin currents, like those generated by laser induced ultrafast demagnetization. A simple procedure for picosecond writing of a six-state memory is described, thus opening the possibility to speed up current logic of electron…
Optical absorption and electron paramagnetic resonance of theEα′center in amorphous silicon dioxide
2008
We report a combined study by optical absorption (OA) and electron paramagnetic resonance (EPR) spectroscopy on the E{sub {alpha}}{sup '} point defect in amorphous silicon dioxide (a-SiO{sub 2}). This defect has been studied in {beta}-ray irradiated and thermally treated oxygen-deficient a-SiO{sub 2} materials. Our results have pointed out that the E{sub {alpha}}{sup '} center is responsible for an OA Gaussian band peaked at {approx}5.8 eV and having a full width at half maximum of {approx}0.6 eV. The estimated oscillator strength of the related electronic transition is {approx}0.14. Furthermore, we have found that this OA band is quite similar to that of the E{sub {gamma}}{sup '} center in…
Dielectric nonlinearity of ferroelectric solid solutions PMN-PZN and PMN-PNN
2001
Abstract Obtaining of novel thin film materials for electrically tuneable capacities is one of the current problems of ferroelectric material application. The most appropriate materials are the ferroelectric lead-containing niobates: PbMg1/3Nb2/3O3 (PMN), PhZn1/3Nb2/3Os (PZN), PbNi1/3Nb2/3O3 (PNN) and their solid solutions were synthesized by solid state reactions at 800–900 °C from oxides. Results of the studies of thermal dependence of dielectric permeability and loss factors of the synthesized solutions are provided together with reciprocal dielectric permeability as function of temperature and electric field intensity. The dielectric characteristics of nonlinear materials are reported e…
X-RAY PHOTOEMISSION ELECTRON MICROSCOPE DETERMINATION OF ORIGINS OF ROOM TEMPERATURE FERROMAGNETISM AND PHOTOLUMINESCENCE IN HIGHCo-CONTENTCoxZn1-xOF…
2014
In this paper, we reported on the X-ray photoemission electron microscope (XPEEM) determination of magnetic and luminescence origins for two CoxZn1-xO films. The cobalt fraction x of radio frequency co-sputtered samples were 0.86(2) and 0.92(2), respectively. Films were ferromagnetic and semiconductive. Unique narrow green color lines beside the ZnO intrinsic emissions were found with a decay time in microsecond range at room temperature. Origins of magnetic and luminescence properties were determined with XPEEM. The X-ray absorption near edge structure at the Co L3-edge denoted that Co was partially oxidized, and phase-contrast images together with chemical composition identification furt…