The chromium reduction from standard worked-out chromium-plating electrolyte containing compounds of trivalent and hexavalent chromium and sulfuric acid is considered. It is shown that the reduction ...of Cr(III) ions with the formation of intermediate adsorbed Cr(II) species is the main electrochemical process. The intermediate species can be further electrochemically reduced to the metal or chemically interact with Cr(VI) species to form a cluster compound, which is stepwise reduced to the metal with a slow transfer of the first electron. Chromium reduction proceeds according to the mechanism of induced codeposition of metals proposed earlier.
This article is a survey on the topic of polynomial amoebas. We review results of papers written on the topic with an emphasis on its computational aspects. Polynomial amoebas have numerous ...applications in various domains of mathematics and physics. Computation of the amoeba for a given polynomial and describing its properties is in general a problem of high complexity. We overview existing algorithms for computing and depicting amoebas and geometrical objects associated with them, such as contours and spines. We review the latest software packages for computing polynomial amoebas and compare their functionality and performance.
The composition and structure of Ni–W alloys prepapred from pyrophosphate electrolyte have been studied. It was demionstrated that, regardless of the deposition current density in the range 2–5 A dm
...–2
, alloys are a single-phase system and represent a solid solution of tungsten in nickel with a face-centered cubic lattice. At low deposition current densities in the coating there exists an impurity oxygen-containing phase of tungsten compounds of an intermediate oxidation state. It was found that the oxygen-containing impurity is distributed unevenly over the coating thickness. Impurity grains are formed only at the initial moment of deposition of the coating at the interface with the substrate together with nickel nanocrystals, and only after some time does the formation of the alloy phase begin. The data obtained are explained in term of the cluster mechanism of induced coprecipitation of alloys of refractory metals with metals of the iron group, proposed earlier.
We present a brief review of investigations and analysis of magnetization curves
M
(
H
) for NiO and ferrihydrite antiferromagnetic nanoparticles in external fields up to 250 kOe. For correct ...interpretation of magnetic properties of systems of antiferromagnetic nanoparticles, it is important to take into account the segment of
M
(
H
) dependences, which corresponds to high fields (exceeding 100 kOe). We analyze the regularities in the formation of additional magnetic subsystems in antiferromagnetically ordered nanoparticles due to the influence of size effects. These additional subsystems (the ferromagnetic subsystem associated with uncompensated magnetic moment and the subsystem of surface free spins) are estimated quantitatively. It is shown that antiferromagnetic nanoparticles with a size of 5 nm acquire the properties of “nanomagnets,” which are not inferior to those for iron-oxide ferromagnetic nanoparticles of the same size.
The optical bound state in the continuum (BIC) is characterized by an extremely high-quality factor resulting in a drastic enhancement of light-matter interaction phenomena. We study the optical ...response of a one-dimensional photonic crystal slab with Kerr focusing nonlinearity in the vicinity of BICs analytically and numerically. We predict a strong nonlinear response including multistable behavior, self-tuning of BICs to the frequency of incident waves, and breaking of symmetry protected BICs. We show that all of these phenomena can be observed in silicon photonic structure at the pump power of several μW/cm2. We also analyze the modulation instability of the obtained solutions and the effect of the finite size of the structure on the stability. Our findings have strong implications for nonlinear photonics and integrated optical circuits.
The influence of the vibration parameters on the electrodeposition of a Ni–SiC composite coating from a vibration-stabilized suspension has been studied. It is shown that an increase in the vibration ...frequency leads to a decrease in the volume fraction of silicon carbide inclusions and a slight increase in the current efficiency. An increase in the vibration amplitude increases the volume fraction of SiC in the composite coating; but, in this case, the coating becomes inhomogeneous and different amounts of silicon carbide particles are deposited on different parts of the samples. Based on the studies performed, a vibration mode was recommended for the deposition of the Ni–SiC coating with a uniform distribution of the silicon carbide particles.
•Magnetic H-T and H-φ phase diagrams of ErB12 include a number of different AF states.•Angular MR and magnetization dependences are highly anisotropic at T < TN.•Dynamic charge stripes in RB12 play a ...key role in the formation of MR anisotropy.•Strong anisotropy in ErB12 is due to the destruction of the RKKY exchange interaction.
The nature of charge transport and magnetization anisotropy was investigated in the ErB12 antiferromagnetic metal with both cooperative Jahn-Teller distortions of the fcc crystal structure and electronic instability (dynamic charge stripes). A butterfly pattern of the H-φ magnetic phase diagram in the (1 1 0) plane was reconstructed, including a large number of different magnetic phases separated from each other by radial and circular boundaries. It is argued that fluctuations of electron density are responsible for the suppression of the indirect Ruderman-Kittel-Kasuya-Yoshida (RKKY) exchange between the nearest neighbored Er3+ ions located along the 〈110〉 directions producing the magnetic phase diversity in ErB12.
—The processes of the formation of Ni–11.5%P–5%W nanocomposite coating during heat treatment of amorphous electrodeposited layers have been studied. The onset crystallization temperature of the ...nanocrystalline Ni
3
P phase has been determined by differential scanning calorimetry. X-ray diffraction analysis showed that heat treatment produces Ni
3
P and, presumably, Ni
5
P
2
phosphides with a size of 5–50 nm according to transmission electron microscopy. The effect of the heat treatment duration on the phase composition and microhardness of coatings has been investigated.
•The M(H) magnetization curves of NiO nanoparticles (NPs) measured in pulsed fields of up to 250 kOe have been studied.•A model of NiO NP obtained from analysis of M(H) data have been ...proposed.•Surface and size effects as well as the origin and the magnitude of uncompensated magnetic moment have been revealed.
-The analysis of the M(H) magnetization curves of antiferromagnetic nanoparticles yields information about magnetic subsystems formed in these objects, which are characterized by a large fraction of surface atoms. However, in the conventionally investigated experimental magnetic field range of up to 60–90 kOe, this analysis often faces the ambiguity of distinguishing the Langevin function-simulated contribution of uncompensated magnetic moments μun of particles against the background of a linear-in-field dependence (the antiferromagnetic susceptibility and other contributions). Here, this problem has been solved using a pulsed technique, which makes it possible to significantly broaden the range of external fields in which the μun contribution approaches the saturation. Nanoparticles of a typical NiO antiferromagnet with an average size of ~ 4.5 nm have been investigated. Based on the thorough examination of the M(H) magnetization curves measured in pulsed fields of up to 250 kOe, a model of the magnetic state of NiO nanoparticles of such a small size has been proposed. The average moment is ~130 μB (μB is the Bohr magneton) per particle, which corresponds to 60–70 decompensated spins of nickel atoms localized, according to the Néel hypothesis (μun~ 3/2), both on the surface and in the bulk of a particle. A part of the surface spins unrelated to the antiferromagnetic core form another subsystem, which behaves as free paramagnetic atoms. Along with the antiferromagnetic core, an additional linear-in-field contribution has been detected, which is apparently related to superantiferromagnetism, i.e., the size effect inherent to small antiferromagnetic particles.
•A sample of NiO nanoparticles with an average size of 8 nm was synthesized.•The sample exhibits the superparamagnetic behavior with a blocking temperature of 185 K.•The magnetization curves in ...fields up to 250 kOe at temperatures of 80–300 K was measured.•The FM, AFM contributions and paramagnetism of the surface spins was extract.
It is well-known that the fraction of surface atoms and the number of defects in an antiferromagnetic particle increase with a decrease in the particle size to tens of nanometers, which qualitatively changes the properties of the particle. Specifically, in antiferromagnetic nanoparticles, spins in the ferromagnetically ordered planes can partially decompensate; as a result, an antiferromagnetic particle acquires a magnetic moment. As a rule, uncompensated chemical bonds of the surface atoms significantly weaken the exchange coupling with the antiferromagnetic particle core, which can lead to the formation of an additional magnetic subsystem paramagnetic at high temperatures and spin-glass-like in the low-temperature region. The existence of several magnetic subsystems makes it difficult to interpret the magnetic properties of antiferromagnetic nanoparticles. It is shown by the example of NiO nanoparticles with an average size of 8 nm that the correct determination of the contributions of the magnetic subsystems forming in antiferromagnetic nanoparticles requires magnetic measurements in much stronger external magnetic fields than those commonly used in standard experiments (up to 60–90 kOe). An analysis of the magnetization curves obtained in pulsed magnetic fields up to 250 kOe allows one to establish the contributions of the uncompensated particle magnetic moment μun, paramagnetic subsystem, and antiferromagnetic particle core. The μun value obtained for the investigated NiO particles is consistent with the Néel model, in which μun ∼ N1/2 (N is the number of magnetically active atoms in a particle), and thereby points out the existence of defects on the surface and in the bulk of a particle. It is demonstrated that the anomalous behavior of the high-field susceptibility dM/dH of antiferromagnetic NiO nanoparticles, which was observed by many authors, is caused by the existence of a paramagnetic subsystem, rather than by the superantiferromagnetism effect.
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