Structural, optical and magnetic properties of nanostructured Cr-substituted Ni-Zn spinel ferrites synthesized by a microwave combustion method

Nanoparticles of Cr3+-substituted Ni-Zn ferrites with a general formula Ni0.4Zn0.6-xCrxFe2O4 (x = 0.0 - 0.6) have been synthesized via a facile microwave combustion route. The crystalline phase has been characterized by XRD, TEM, FT-I and XPS revealing the spinel ferrite structure without extra phases. Crystallite sizes of 23 - 32 nm as estimated by XRD analyses, after corrections for crystal stains by Williamson-Hall method, are comparable to the average particle sizes observed by TEM which indicates successfully synthesized nanocrystals. Rietveld refinement analyses of the XRD patterns have inferred a monotonic decrease behavior of the lattice parameter with Cr doping in agreement with Vegard's law of solid solution series. Furthermore, cations distribution with an increased inversion factor indicate the B-site preference of Cr3+ ions. The oxidation states and cations distribution indicated by XPS results imply the Cr3+ doping on the account of Zn2+ ions and a partial reduction of Fe3+ to Fe2+ to keep the charge balance in a composition series of (Ni2+)0.4(Zn2+, Cr3+)0.6(Fe2+, Fe3+)2(O2-)4. The optical properties were explored by optical UV-Vis spectroscopy indicating allowed direct transitions with band gap energy that decreases from 3.9 eV to 3.7 eV with Cr doping. Furthermore, the photocatalytic activity for the degradation of methyl orange (MO) dye was investigated showing largely enhanced photodecomposition up to 30% of MO dye over Ni0.4Cr0.6Fe2O4 for 6 hours. A vibrating sample magnetometry (VSM) measurements at room temperature show further enhancement in the saturation magnetization of Ni0.4Zn0.6Fe2O4 , the highest in Ni-Zn ferrites, from about 60 to 70 emu/g with the increase of Cr concentration up to x = 0.1, while the coercivity shows a general increase in the whole range of Cr doping.Comment: 21 page, 9 figure

Doping Dependence of the in-Plane Transition in Co3_3Sn2_2S2_2

In Co$_3$Sn$_2$S$_2$ two transitions are observed, the main one to a ferromagnetic state at $T_C = 174$ K and the second one, involving in-plane components at $T_P = 127$ K. We follow their doping dependence as Sn is replaced with In, which causes a reduction of $T_C$ and $T_P$. Importantly, both transitions follow the same doping dependence, indicating a single energy scale involved with both processes.Comment: accepted as a short note in JPSJ; a continuation of work published in arXiv:2211.01483 and https://doi.org/10.1103/PhysRevB.106.L18040

Structural, Optical and Single-domain Magnetic Features of the Noncollinear Ferrimagnetic Nano-spinel Chromites ACr2_2O4_4 (A = Ni, Co, and Mn)

Spinel chromites ACr$_2$O$_4$ with inherent magnetic geometrical frustration usually exhibit a noncollinear ferrimagnetic ground state when A are magnetic ions, with possibly crystallite-size dependent intriguing magnetic features. Here, we report single-domain magnetic properties of ACr$_2$O$_4$ (A = Ni, Co, and Mn) nanocrystals, with an average crystallite size of 18, 15 and 10 nm, exhibiting an optical energy gap of 2.87, 3.05 and 2.9 eV, respectively. The temperature dependence of magnetization indicates the main bulk magnetic transitions with a commonly coexisting spin-glass-like state and finite-size effects on the noncolinear ferrimagnetic transitions. An anomaly observed at Ts = 15, 24 and 10 K is attributed to the bulk magnetic transition to a canted antiferromagnetic state in NiCr$_2$O$_4$ and incommensurate spiral orders in CoCr$_2$O$_4$ and MnCr$_2$O$_4$ NCs, respectively. A further bulk magnetic transition to a commensurate spiral order is observed for CoCr$_2$O$_4$ NCs at a lock-in temperature Tl = 5 K much lower than that reported using bulk samples, while it is completely suppressed in the MnCr$_2$O$_4$ NCs. Finite-size effects and single-domain magnetic behaviors indicated by anomalous temperature-dependences of the coercive field and the hysteresis-loop squareness, mainly driven by a magnetocrystalline anisotropy, are discussed in comparison to results reported using bulk counterparts

Effect of applying static electric field on the physical parameters and dynamics of laser-induced plasma

AbstractIn order to improve the performance of the LIBS technique – in particular its sensitivity, reproducibility and limit of detection – we studied the effect of applying a static electric field with different polarities on the emission spectra obtained in a typical LIBS set-up. The physical parameters of the laser-induced plasma, namely the electron density Ne and the plasma temperature Te, were studied under such circumstances. In addition to the spectroscopic analysis of the plasma plume emission, the laser-induced shock waves were exploited to monitor the probable changes in the plasma plume dynamics due to the application of the electric field. The study showed a pronounced enhancement in the signal-to-noise (S/N) ratio of different Al, neutral and ionic lines under forward biasing voltage (negative target and positive electrode). On the other hand, a clear deterioration of the emission line intensities was observed under conditions of reversed polarity. This negative effect may be attributed to the reduction in electron-ion recombinations due to the stretched plasma plume. The plasma temperature showed a constant value in the average with the increasing electric field in both directions. This effect may be due to the fact that the measured values of Te were averaged over the whole plasma emission volume. The electron density was observed to decrease slightly in the case of forward biasing while no significant effect was noticed in the case of reversed biasing. This slight decrease in Ne can be interpreted in view of the increase in the rate of electron–ion recombinations due to the presence of the electric field. No appreciable effects of the applied electric field on the plasma dynamics were noticed

3-Chloro-4-methyl­quinolin-2(1H)-one

The title compound, C10H8ClNO, is almost planar (r.m.s. deviation for the 13 non-H atoms = 0.023 Å). In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds generate R 2 2(8) rings. Weak aromatic π–π stacking inter­actions [centroid–centroid distance = 3.7622 (12) Å] also occur

Adaptation to Blue Light in Marine Synechococcus Requires MpeU, an Enzyme with Similarity to Phycoerythrobilin Lyase Isomerases

Marine Synechococcus has successfully adapted to environments with different light colors, which likely contributes to this genus being the second most abundant group of microorganisms worldwide. Populations of Synechococcus that grow in deep, blue ocean waters contain large amounts of the blue-light absorbing chromophore phycourobilin (PUB) in their light harvesting complexes (phycobilisomes). Here, we show that all Synechococcus strains adapted to blue light possess a gene called mpeU. MpeU is structurally similar to phycobilin lyases, enzymes that ligate chromophores to phycobiliproteins. Interruption of mpeU caused a reduction in PUB content, impaired phycobilisome assembly and reduced growth rate more strongly in blue than green light. When mpeU was reintroduced in the mpeU mutant background, the mpeU-less phenotype was complemented in terms of PUB content and phycobilisome content. Fluorescence spectra of mpeU mutant cells and purified phycobilisomes revealed red-shifted phycoerythrin emission peaks, likely indicating a defect in chromophore ligation to phycoerythrin-I (PE-I) or phycoerythrin-II (PE-II). Our results suggest that MpeU is a lyase-isomerase that attaches a phycoerythrobilin to a PEI or PEII subunit and isomerizes it to PUB. MpeU is therefore an important determinant in adaptation of Synechococcus spp. to capture photons in blue light environments throughout the world\u27s oceans