Vasiliy O. Pelenovich

Spin cycloid destruction in Pr doped BiFeO3 films studied by conversion-electron Mossbauer spectroscopy

Crystalline Bi1−xPrxFeO3 films were fabricated on Si (100) substrates by sol-gel technique. X-ray diffraction revealed a decrease of lattice constants of the doped samples evidencing substitution of Bi by Pr ions. Ferromagnetism with low saturation magnetization Ms = 1–3 emu/cm3 of the films were observed by Vibrating sample magnetometry. Systematic change of Mossbauer parameters of the films with Pr doped concentration increase were obtained by Conversion-electron Mossbauer spectroscopy (CEMS). The results of both one- and two-sextet fittings of the CEMS spectra provide evidence for destruction of the spin cycloid in Pr-doped BiFeO3.

MoS2 memristor with photoresistive switching.

A MoS2 nanosphere memristor with lateral gold electrodes was found to show photoresistive switching. The new device can be controlled by the polarization of nanospheres, which causes resistance switching in an electric field in the dark or under white light illumination. The polarization charge allows to change the switching voltage of the photomemristor, providing its multi-level operation. The device, polarized at a voltage 6 V, switches abruptly from a high resistance state (HRSL6) to a low resistance state (LRSL6) with the On/Off resistance ratio of about 10 under white light and smooth in the dark. Analysis of device conductivity in different resistive states indicates that its resistive state could be changed by the modulation of the charge in an electric field in the dark or under light, resulting in the formation/disruption of filaments with high conductivity. A MoS2 photomemristor has great potential as a multifunctional device designed by using cost-effective fabrication techniques.

Magnetooptics of non-Kramers Eu3+ ions in garnets: analysis complemented by crystal-field splitting modeling calculations

Abstract Spectra of absorption, luminescence, magnetic circular dichroism (MCD), and magnetic circular polarization of luminescence (MCPL) in Gd 3 Ga 5 O 12 :Eu 3+ and Eu 3 Ga 5 O 12 garnets were studied within the visible spectral range at 300 K. Analysis of the spectral and temperature dependences of the magnetooptical and optical spectra made it possible to identify the magneto-dipole (MD) and electro-dipole (ED) 4f→4f transitions occurring between Stark sublevels of the 7 F J ( J =1, 2) and 5 D 0 multiplets in Eu 3+ -containing garnet structures. Quantum mechanical “mixing” had significant influence on quasi-degenerate states of the non-Kramers rare-earth Eu 3+ ion for Eu 3 Ga 5 O 12 in MCD due to forbidden MD transition 7 F 1 → 5 D 0 and for Gd 3 Ga 5 O 12 :Eu 3+ in MCPL due to MD 4f→4f transition 5 D 0 → 7 F 1 and forced ED-transition 5 D 0 → 7 F 2 . A parameterized Hamiltonian defined to operate within the entire 4f (6) ground electronic configuration of Eu 3+ ion was used to model the experimental Stark levels, including their irreducible representations and wavefunctions. The crystal-field parameters were determined through a Monte-Carlo method in which nine independent crystal-field parameters, B k q , were given random starting values and optimized using standard least-squares fitting between calculated and experimental levels. The final fitting standard deviation between 57 calculated-to-experimental levels was 0.73 meV.

Magnetooptics of magnetic-dipole transitions in the rare-earth paramagnetic garnets

The Faraday effect (FE) of the rare-earth (RE) paramagnetic garnet crystals associated with magnetic-dipole (MD) transitions has been investigated theoretically over a wide temperature range 80 to 300 K. Over this temperature range, the “gyromagnetic” Verdet Vgm(m) of the Eu3Ga5O12 (EuGG) is not a linear function of the magnetic susceptibility χ measured along the [111] axis. We find that the nontrivial character of the temperature dependence of the MD Verdet constant Vgm(m) is associated with the presence of a contribution to the Faraday rotation of the Van Vleck “mixing” by an external magnetic field of the Eu3+ electronic states. The optical absorption and magnetic circular dichroism (MCD) of Eu3+ ion in EuGG at 85 K for the MD transition 7F0 → 5D1 were measured along the [111] axis. We show that the appearance of the MCD feature observed for the absorption line near 526.6 nm for the 7F0 → 5D1 MD absorption band may be well-explained by the contribution of Van Vleck “mixing” between the Stark singlet states from the 7F0 and 7F1 multiplet manifolds mixed by the external magnetic field H.

Enhanced visible light photodegradation activity of RhB/MB from aqueous solution using nanosized novel Fe-Cd co-modified ZnO

A series of novel Fe-Cd co-doped ZnO nanoparticle based photocatalysts are successfully synthesized by sol-gel route and characterized using scanning electron microscopy (SEM), energy dispersive X-ray emission (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-Vis spectroscopy, X-ray photoelectron spectroscopy (XPS), and Brunauer-Emmett-Teller (BET) techniques. The photocatalytic activity of ZnO nanoparticles doped with various atomic weight fraction of Fe and Cd has been investigated under visible light irradiation using the Methylene Blue and Rhodamine B dye in aqueous solution. The FeCd (2%):ZnO (ZFC-1) exhibit the highest photocatalytic activity in terms of rate constant as KMB = 0.01153 min−1 and KRhB = 0.00916 min−1). Further, the re-usability of the ZFC-1 photocatalyst is studied which confirms that it can be reused up to five times with nearly negligible loss of the photocatalytic efficiency. Moreover, the role of photoactive species investigated using a radical scavenger technique. The present investigations show that the doping concentration plays significant role in photocatalytic performance. The visible light absorption shown by Fe-Cd co-doped ZnO nanoparticles is much higher than that of undoped body probably due to co-doping, and the charge carrier recombination is decreased effectively which yields a higher photocatalytic performance. The mechanism for the enhancement of photocatalytic activity under visible light irradiation is also proposed.

Growth and magnetooptical properties of anisotropic TbF3 single crystals

This paper investigates the Faraday effect and absorption and luminescence spectra of single-crystal TbF3 measured at 90 K and 300 K. The optical-quality single-phase TbF3 crystals (structural type β-YF3) were grown by the Bridgman technique. Faraday rotation angles were measured at remagnetization along the [100] crystallographic axis. Low temperature optical measurements were carried out along the [100] axis. “Quasi-doublet” sublevels with energy at 0 cm−1, 65 cm−1, and 190 cm−1, and also a singlet sublevel with energy at 114 cm−1 located in the ground 7F6 multiplet were determined from the low temperature luminescence spectra. The Van-Vleck behavior of the magnetic susceptibility χb can be satisfactorily explained by the magnetic mixing of wave functions belonging to the ground and first excited “quasi-doublet” sublevels at 0 and 65 cm−1, respectively. Analysis of the oscillation dependences of the rotation angle showed that the value of the natural birefringence (Δn ≈ 0.0186) remains nearly constant within the wavelength and temperature ranges under investigation. As the temperature decreases, we find significant increases in the oscillation amplitude of the rotation angle and in the Verdet constant V. The spectral dependences V(χ) are linear throughout the temperature range. The magnetooptical activity of TbF3 can be explained by means of the spin- and parity-allowed electric-dipole 4f → 5d transitions in the Tb3+ ions.This paper investigates the Faraday effect and absorption and luminescence spectra of single-crystal TbF3 measured at 90 K and 300 K. The optical-quality single-phase TbF3 crystals (structural type β-YF3) were grown by the Bridgman technique. Faraday rotation angles were measured at remagnetization along the [100] crystallographic axis. Low temperature optical measurements were carried out along the [100] axis. “Quasi-doublet” sublevels with energy at 0 cm−1, 65 cm−1, and 190 cm−1, and also a singlet sublevel with energy at 114 cm−1 located in the ground 7F6 multiplet were determined from the low temperature luminescence spectra. The Van-Vleck behavior of the magnetic susceptibility χb can be satisfactorily explained by the magnetic mixing of wave functions belonging to the ground and first excited “quasi-doublet” sublevels at 0 and 65 cm−1, respectively. Analysis of the oscillation dependences of the rotation angle showed that the value of the natural birefringence (Δn ≈ 0.0186) remains nearly constant w...

Design and experimental testing of a gas cluster ion accelerator

A gas cluster ion beam (GCIB) system with cluster energy up to 12 keV has been designed. To facilitate pumping of the nozzle chamber and increased pressure of the gas source up to 10 atm, pulse mode was used for the gas feeding. Argon was employed as the working gas. To separate monomers from clusters, both electromagnet and retarding electrode were utilized. A maximal pulsed cluster current of 90 nA has been achieved. The shape of pulsed ion beam currents has been analyzed in detail at different applied magnetic and retarding electric fields.

Corrigendum: MoS 2 memristor with photoresistive switching

Scientific Reports 6: Article number: 3122410.1038/srep31224; published online: August 05 2016; updated: November 14 2015

Optical and magnetic properties of InFeP layers prepared by Fe+ implantation

InFeP layers are prepared by ion implantation of InP with 100-keV Fe+ ions to a dose of 5 × 1016 cm−2 and investigated by optical, magnetic, and ion beam analysis measurements. Photoluminescence measurements show a deep-level peak at 1.035 eV due to Fe in InP and two exciton-related luminescences at 1.426 eV and 1.376 eV in the implanted samples annealed at 400 °C. Conversion electron Mossbauer spectroscopy reveals a doublet corresponding to Fe3+ ions in the indium sites. Atomic force microscopy and magnetic force microscopy show that magnetic clusters are formed in the annealing process. The magnetization-field hysteresis loops show ferromagnetic properties persisting up to room temperature with a coercive field of 100 Oe (1 Oe = 79.5775 A·m−1), saturation magnetization of 4.35 × 10−5 emu, and remnant magnetization of 4.4 × 10−6 emu.