Browsing by Author "Moșneaga, Vasilii"

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CHARACTERIZATION OF GEOMETRICALLY FRUSTRATED Zn1−xMnxAl2O4 THIN FILMS PREPARED BY METALORGANIC AEROSOL DEPOSITION
(2009) Sanchez, Rodolfo; Saleta, Martin Eduardo; Șapoval, Oleg; Gehrke, Kai; Moșneaga, Vasilii; Samwer, Konrad
We present the results on the structure and magnetoelectric properties of Zn1−xMnxAl2O4 thin films (0 ≤ x ≤ 1), prepared by metalorganic aerosol deposition (MAD) technique. The films have been grown epitaxially on MgO(100) substrates and characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDX), magnetization, electron paramagnetic resonance (EPR) and capacitance as a function of temperature and magnetic field. For large x values (x = 0.75 and 1), we observed a deviation of the magnetization from a Curie-Weiss law below 40K, indicating the expected magnetic ordering of the spinel. In the proximity of this magnetic characteristic temperature the capacitance as a function of temperature shows a peak, which infers a multiferroic character of these spinels.
DEVELOPMENT OF MATERIALS FOR THERMOELECTRIC GENERATORS: SUPERLATTICE Ca3Co4O9-Sr3Co4O9
(Editura "Tehnica-UTM", 2015-05-20) Șapoval, Oleg; Belenciuc, Alexandr; Jooss, Christian; Roddatis, Vladimir; Moșneaga, Vasilii
We have prepared multilayered structures composed from misfit layered Ca- and Sr- cobaltates by Metalorganic Aerosol Deposition technique. X-ray and Transmission Electron Microscopy analyzes confirms the forming superlattice along c direction from common CoO2 interlayers and alternating Ca2CoO3 and Sr2CoO3 layers with periodicity of 4-6 unit cell. Our results indicate the possibility to fabricate artificial material on the base of layered cobaltates for thermoelectric applications.
GIANT NEGATIVE PHOTOCONDUCTIVITY IN La 0.7Ca0.3MnO3 THIN FILMS
(2004) Moșneaga, Vasilii; Giske, Arnold; Samwer, Konrad; Mișina, Elena; Tamura, Takehisa; Nakabayashi, Seiichiro; Belenciuc, Alexandr; Șapoval, Oleg; Culiuc, Leonid
The increase of the resistance up to two orders of magnitude under laser illumination (l5760 nm) was observed in La0.7Ca0.3MnO3 ~LCMO! epitaxial thin films in ferromagnetic state.Optical absorption also increases by 10–15 % and the magnetic second-harmonic generation signal decreases down to zero under the irradiation. The light induced changes are reversible with decreases down to zero under the irradiation. The light induced changes are reversible with characteristic relaxation times t;1 – 30 s. Magnetic field, B54 T, suppresses the photoconductivity and decreases its relaxation time. Photoinduced effects are caused by the injection of a large number of extra carriers, which change the ~antiferromagnetic! AFM/FM phase balance in LCMO, favoring the insulating AFM state.
INTERFACE-CONTROLLED MAGNETISM AND TRANSPORT OF ULTRATHIN MANGANITE FILMS
(2013) Șapoval, Oleg; Huhn, Sebastian; Verbeeck, Johann; Jungbauer, Markus; Belenciuk, Alexandr; Moșneaga, Vasilii
We report ferromagnetic, T C ¼ 240 K, and metallic, T MI ¼ 250 K, behaviors of a three unit cell thick interface engineered lanthanum manganite film, grown by metalorganic aerosol deposition technique on SrTiO 3(100) substrates. Atomically resolved electron microscopy and chemical analysis show that ultrathin manganite films start to grow with La-O layer on a strongly Mn/Ti-intermixed interface, engineered by an additional deposition of 2 u.c. of Sr-Mn-O. Such interface engineering results in a hole-doped manganite layer and stabilizes ferromagnetism and metallic conductivity down to the thickness of d ¼ 3 u.c. The films with d ¼ 8 u.c. demonstrate a metallic conductivity down to the thickness of d ¼ 3 u.c. bulk-like transport behavior with TMI T C ¼ 310330 K.
MAGNETOTRANSPORT PROPERTIES OF ULTRATHIN LaMnO3 LAYERS
(Technical University of Moldova, 2011-07-07) Șapoval, Oleg; Belenciuc, Alexandr; Zasavițchi, Efim; Canțer, Valeriu; Moșneaga, Vasilii
We report the transport and magnetic properties of La-deficient ultrathin films of La1-MnO3 (LMO) grown on SrTiO3 (STO) and engineered by using different interfacial layers. LMO layer and adjusting interface oxide (LaO-STO and SMO) layers were grown by a metalorganic aerosol deposition technique with monolayer accuracy. The role of LaO-TiO2 interface in the formation of ferromagnetic metallic state in very thin LMO films was demonstrated. Ferromagnetic metallic ground state in LMO films with the thickness down to 6 monolayers is stabilized by a combination of a La-deficiency and the interface-induced doping.
ORIENTATION-DEPENDENT OXYGEN EVOLUTION ACTIVITY OF EPITAXIAL RUDDLESDEN−POPPER PR 0.5Ca1.5MnO4 THIN FILMS
(2024) Ottinger, Natalie; Belenciuc, Alexandr; Șapoval, Oleg; Hausmann, Christopher; Moșneaga, Vasilii; Jooss, Christian; Qian, Ma; Fatemeh, Ebrahimi
Studying the oxygen evolution reaction (OER) on anisotropic perovskite oxides with different surface orientations improves our understanding of how surface structure, chemistry, catalytic stability, and activity are related. Here, we present a comparative electrochemical study of(001)- and (010)-oriented epitaxial thin films of Ruddlesden−Popper (n = 1) Pr0.5Ca1.5MnO4(RP-PCMO) grown on Nb:SrTiO3 (STNO) substrates of different orientations with using buffer layers. The results on epitaxial films are compared with those of the RP-PCMO powder. The OER activity and stability are studied using cyclic voltammetry and rotating ring disk electrodes under alkaline conditions. In addition, an analysis of their surface structure and chemistry by AFM and XPS before and after electrochemical measurements was carried out. The RP-PCMO powder shows high stability during electrochemical cycling. In contrast, the two differently oriented thin films are both corroding, while the (010)-oriented films reveal a higher activity and stability than the (001)-oriented ones. The variation in electrochemical activity and stability of the polycrystalline and single-crystalline RP-PCMO electrodes of different orientations is related to their different surface chemistry. In particular, it depends on the different Mn/Pr/Ca ratios and their different rates of Ca leaching, which is governed by the orientation-dependent Ca hydroxide surface concentration.