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[en] The puzzle of three-dimensional magnetic interactions in the structurally two-dimensional layered-oxide NaxCoO2 is addressed using first-principles calculations and an analysis of the exchange mechanisms. The calculations agree with recent neutron results, favoring the antiferromagnetic stacking of ferromagnetic planes. The superexchange via direct O-O hopping and through intermediate Na sp2 hybrids couples each Co to its nearest and six next-nearest interplanar neighbors via equivalent paths. The individual exchange constants are rather two-dimensional, like the lattice itself, but due to multiple c-axis exchange paths, the magnetism becomes effectively three-dimensional.
[en] We report on the control of magnetization reversal in exchange-biased Co/CoO nanorings resulting from the competition between field-cooling-induced unidirectional anisotropy at the Co/CoO interface and shape anisotropy of the elongated Co nanorings. We observed that the magnetization reversal mechanisms and magnitudes of exchange bias fields are strongly dependent on the strength and orientation of the cooling field relative to the major axis of the nanorings. Our results demonstrate a convenient technique to control the magnetization reversal modes in ferromagnetic nanorings.
[en] Highlights: • A simple, cheap and environmental friendly polyol method has been used to prepare samples. • The FeCo samples show large Ms which is required in different industry areas. • In Fe55Co45 sample, the Ms of 273 emu/g has been obtained which is the largest reported values. FeCo nanoparticles with different compositions were prepared by a polyol reduction method and annealed in gas mixtures. All FeCo nanoparticles show large saturation magnetization (over 220 emu/g). The largest saturation magnetization of 273 emu/g was observed in the Fe55Co45 sample. As for Fe48Co52, the impurity phase of CoFe2O4 existed when nanoparticles were annealed at low temperature (200–400 °C). While annealed at above 450 °C, pure Fe48Co52 nanoparticles with large saturation magnetization of 230 emu/g were obtained. These FeCo nanoparticles with large saturation magnetization have great potential in some industry fields.
[en] It is shown that magnetoreflectance of natural light up to +4% exists in magnetostrictive ferrimagnetic spinel CoFe2O4 single crystal; this effect is associated with a change of the fundamental absorption edge, the impurity absorption band, and the phonon spectrum under the action of a magnetic field. The correlation between the field dependences of magnetoreflectance and magnetostriction has been established. The physical mechanisms responsible for the spectral and field peculiarities of magnetoreflection have been explained. It is shown that the magnetorefractive effect in CoFe2O4, which is associated with magnetoelastic properties of the spinel, amounts to +1.5 × 10–3 in magnetic fields exceeding the saturation field. Analysis of magnetooptical and magnetoelastic data has made it possible to estimate deformation potential as Ξu = 20 eV for the valence band of the spinel.
[en] A study of the magnetization reversal process in a co-precipitated cobalt ferrite material at 300 K was carried out. The evolution of the reversible Mrev and irreversible Mirr magnetization components were determined by measuring sets of recoil curves from different points on the initial magnetization curve and demagnetization curve. From these data, Mrev(Mirr)Hi curves were built, being Hi the internal field of the sample. The interrelation function η=(Mrev/Mirr)Hi was determined as well. The results suggest that domain wall movement subject to pinning is the dominant mechanism for the reversal magnetization process in this material
[en] It is the first report on the recording performance of a perpendicular metal evaporated (ME) tape measured with a giant magnetoresistive head. To solve the application difficulty of oblique evaporated tape media to linear scan tape systems, a perpendicular evaporated Co-CoO tape was proposed instead. The prepared sample showed perpendicular anisotropy with coercivity of 107.3 kA/m, Mrt of 3.9 mA and squareness of 0.25. Identical recording characteristics were obtained for both head-media moving directions, which enables the application of perpendicular evaporated Co-CoO tape to linear scan tape systems. The better carrier-to-noise ratio was also confirmed by comparison with a current advanced product of metal particulate tape, which can realize the higher recording density of linear scan tape systems using ME tape
[en] The objective of this research was to study the inhibitory effect of CoO in ZnO obtained by solution combustion synthesis (SCS) when they are incorporated into alkyd formulations. ZnO and mixed oxides of the type Zn1-xCoxO (where x = 0.05-0.10-0.15-0.20) were obtained by SCS and characterized by XRD, ICP-OES, SEM and TEM. The pigments were incorporated into alkyd primers in three proportions, 5%, 10% and 20% by weight pigments / resin. Steel probes protected with the alkyd formulations were tested in salt spray and sulfur dioxide chambers. Likewise, the inhibiting efficiency of the pigments was estimated by electrochemical tests (Tafel method) in 0.1 M NaCl solution. The results showed that CoO improves the inhibitory properties of the ZnO based nano-pigments obtained by SCS.
[es]El objetivo de esta investigación ha sido estudiar el efecto inhibidor del CoO en ZnO obtenidos por síntesis por combustión de solución (SCS) cuando son incorporados a formulaciones alquídicas. ZnO y óxidos mixtos del tipo Zn1-xCoxO (donde x = 0,05-0,10-0,15-0,20) fueron obtenidos por SCS y caracterizados por XRD, ICP-OES, SEM y TEM. Los pigmentos fueron incorporados a imprimantes alquídicos medios en aceite en tres proporciones de 5%, 10% y 20% en peso pigmentos/resina. Probetas de acero protegidas con las formulaciones alquídicas fueron ensayadas en cámaras de niebla salina y dióxido de azufre. Asimismo, la eficiencia inhibidora de los pigmentos fue estimada mediante ensayos electroquímicos (método de Tafel) en solución 0,1 M de NaCl. Los resultados mostraron que el CoO mejora las propiedades inhibidoras de los nano-pigmentos base ZnO obtenidos por SCS.
[en] Hexagonal flake Co3O4 was prepared by calcining Co-MOF precursors in air. Co3O4@PANI was obtained via hydrothermal and oxidative polymerization processes, and the electromagnetic wave absorption properties of the composites were investigated. Scanning emission microscopy and transmission electron microscopy images show that hexagonal flake Co3O4 possesses a diameter in the range of 2–4 µm and a side length 550–950 nm. With the decrease in Co3O4 content, the absorption performance of Co3O4@PANI increases gradually. When the mass ratio of Co3O4 to PANI is 1:8, the minimum reflection loss value is − 37.39 dB at 7.28 GHz with a layer thickness of 4 mm. Co3O4@PANI also has effective absorption with the entire test thickness, and the maximum absorption bandwidth can reach 3.52 GHz. Therefore, the as prepared hexagonal flake Co3O4@PANI has potential for application in the field of electromagnetic wave absorption.
[en] We present the observation of a double hysteresis loop behavior in oxidized Co nanocluster assembled films. These films consist of ferromagnetic Co clusters of about 2 nm diameter, embedded in a thin antiferromagnetic CoO matrix. Magnetization measurements after zero field cooling from 300 to 5 K show this double loop behavior, with remanent magnetization of the sample determining the point of loop separation. Such magnetization behavior is related to the presence of two ferromagnetic parts with antiparallel orientations of their magnetization vectors. While the loop shifts are provided via the exchange bias mechanism, the alignment of randomly oriented magnetization vectors of Co clusters in either of two directions suggests the presence of an exchange spring effect in the system
[en] Three-dimensional porous nickel foam was used as a current collector to prepare a Co-Ni oxide/Ni foam electrode for a supercapacitor. The synthesized Co-Ni oxide was proven to consist of mixed oxide phases of Co3O4 and NiO. The Co-Ni oxide/Ni foam electrode prepared was characterized by morphological observation, crystalline property analysis, cyclic voltammetry, and impedance spectroscopy. Cyclic voltammetry for the electrode showed high specific capacitances, such as 936 F g-1 at 5 mV s-1 and 566 F g-1 at 200 mV s-1, and a comparatively good cycle performance. These improved results were mainly due to the dimensional stability of the nickel foam and its high electrical contact between the electrode material and the current collector substrate