Magnetic structure of bulk GdMnO₃: Influence of strain

Internal structural distortions are of great interest in the determination of electronic and magnetic properties of the strong correlated rare earth manganites. When combined with external structural modifications like uniaxial or biaxial strains, structural distortions can lead to the emergence of new magnetic ground states. This realization is seemingly more probable with the low-band-width manganite GdMnO3 on the grounds that it is located in the magnetoelectric phase diagram of orthorhombic rare earth manganites between the A-type antiferromagnetic (AFM) order and the cycloidal spin orders. Herein, a thorough analysis of the magnetic structure of GdMnO3 based on the density functional theory connected with a classical Heisenberg model together with Monte Carlo calculations is presented. It is found whether a compressive uniaxial strain along the c direction or biaxial strain on the ab plane favors a ferromagnetic (FM) ground state over the AFM one. On the contrary, a tensile strain also on the ab plane is likely to stabilize the E-type AFM order

Electronic and magnetic properties of BaFeO₃ on the Pt(111) surface in a quasicrystalline approximant structure

Perovskite‐like ABO3 oxides A = (Ca, Sr, Ba) and B = (Ti, Mn, Fe, Co, Ni) show a large variety of structures and physical properties. Among them is BaTiO3 (BTO), one of the most investigated and used perovskites. In a BTO film on Pt(111), the first oxide quasicrystal was discovered. Herein, by means of first‐principle methods, the cubic and hexagonal phases of bulk BaFeO3 (BFO) are investigated. Both phases show ferromagnetic order. Monolayers and double layers of BFO are studied on a Pt(111) surface. The double‐layer configuration of the cubic and hexagonal phases is structurally inequivalent but both double‐layer films show antiferromagnetic order. In analogy to the BTO quasicrystal approximant structure on Pt(111), a corresponding BFO structure is investigated. The Fe atoms are surrounded by three oxygen atoms and the resulting FeO3 units are separated by barium atoms with the total stoichiometry Ba5Fe4O12

Study of the Negative Magneto-Resistance of Single Proton-Implanted Lithium-Doped ZnO Microwires

The magneto-transport properties of single proton-implanted ZnO and of Li(7\%)-doped ZnO microwires have been studied. The as-grown microwires were highly insulating and not magnetic. After proton implantation the Li(7\%) doped ZnO microwires showed a non monotonous behavior of the negative magneto-resistance (MR) at temperature above 150 K. This is in contrast to the monotonous NMR observed below 50 K for proton-implanted ZnO. The observed difference in the transport properties of the wires is related to the amount of stable Zn vacancies created at the near surface region by the proton implantation and Li doping. The magnetic field dependence of the resistance might be explained by the formation of a magnetic/non magnetic heterostructure in the wire after proton implantation.Comment: 6 pages with 5 figure

Lattice dynamics and structural stability of ordered Fe3Ni, Fe3Pd and Fe3Pt alloys

We investigate the binding surface along the Bain path and phonon dispersion relations for the cubic phase of the ferromagnetic binary alloys Fe3X (X = Ni, Pd, Pt) for L12 and DO22 ordered phases from first principles by means of density functional theory. The phonon dispersion relations exhibit a softening of the transverse acoustic mode at the M-point in the L12-phase in accordance with experiments for ordered Fe3Pt. This instability can be associated with a rotational movement of the Fe-atoms around the Ni-group element in the neighboring layers and is accompanied by an extensive reconstruction of the Fermi surface. In addition, we find an incomplete softening in [111] direction which is strongest for Fe3 Ni. We conclude that besides the valence electron density also the specific Fe-content and the masses of the alloying partners should be considered as parameters for the design of Fe-based functional magnetic materials.Comment: Revised version, accepted for publication in Physical Review

Genotoxic and Histopathological Effects of Chlorpyrifos on African Catfish, C. gariepinus and Ameliorative Potentials of Ackee Apple, blighia sapida Seed

Chlorpyrifos (CPF) is a very toxic pesticide commonly used for controlling agriculturally important pests. The present study investigates DNA damaging effects of CPF on Clarias gariepinus was assessed using genetic assays. Fish were exposed to varying concentrations of CPF (100ppm, 200ppm and 300ppm) at 96 hours (acute exposure). LC50 of the pesticide was found to be 120ppm and one-tenth of the LC50 (12ppm) was taken for the chronic exposure. Distilled water and colchicine were used as negative and positive controls respectively. After 28 days of chronic exposure, fish were fed with inclusion of B. sapida seed (powder) for 14 days. Liver and gills of the fish were removed following 96h exposure, days 7, 14 and 28 of the chronic exposure as well as after the period of amelioration (14 days) for CA assay and histopathological analysis. The results of CA assay showed statistically significant (p ˂ 0.05) increase in CA in a dose-dependent manner for all the exposed groups after acute exposure and time dependent after chronic exposure. Also, this study showed that CPF can potentially induce genotoxic and histopathological changes in fish and other aquatic organisms

Advances in methods to obtain and characterise room temperature magnetic ZnO

We report the existence of magnetic order at room temperature in Li-doped ZnO microwires after low energy H+ implantation. The microwires with diameters between 0.3 and 10 μm were prepared by a carbothermal process. We combine spectroscopy techniques to elucidate the influence of the electronic structure and local environment of Zn, O, and Li and their vacancies on the magnetic response. Ferromagnetism at room temperature is obtained only after implanting H+ in Li-doped ZnO. The overall results indicate that low-energy proton implantation is an effective method to produce the necessary amount of stable Zn vacancies near the Li ions to trigger the magnetic order.Fil: Lorite, I.. Fakultät für Physik und Geowissenschaften; AlemaniaFil: Straube, Benjamin. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Ohldag, H.. University Of Stanford; Estados UnidosFil: Kumar, P.. Fakultät für Physik und Geowissenschaften; AlemaniaFil: Villafuerte, Manuel Jose. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Esquinazi, P.. Fakultät für Physik und Geowissenschaften; AlemaniaFil: Rodriguez Torres, Claudia Elena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico La Plata. Instituto de Física La Plata; ArgentinaFil: Perez de Huelani, S.. Universidad Nacional de Tucumán. Facultad de Ciencias Exactas y Tecnología. Departamento de Física. Laboratorio de Física del Solido; ArgentinaFil: Antonov, V. N.. Institute for Metal Physics; Ucrania. Max Planck Institut für Mikrostrukturphysik; AlemaniaFil: Bekenov, L. V.. Institute for Metal Physics; Ucrania. Max Planck Institut für Mikrostrukturphysik; AlemaniaFil: Ernst, A.. Max Planck Institut für Mikrostrukturphysik; Alemania. Universitat Leipzig; AlemaniaFil: Hoffmann, M.. Max Planck Institut für Mikrostrukturphysik; Alemania. Martin Luther University Halle-Wittenberg; AlemaniaFil: Nayak, S. K.. Martin Luther University Halle-Wittenberg; AlemaniaFil: Adeagbo, W. A.. Martin Luther University Halle-Wittenberg; AlemaniaFil: Fischer, G.. Max Planck Institut für Mikrostrukturphysik; AlemaniaFil: Hergert. W.. Martin Luther University Halle-Wittenberg; Alemani

Quasicrystals and their approximants in 2D ternary oxides

2D oxide quasicrystals (OQCs) are recently discovered aperiodic, but well-ordered oxide interfaces. In this topical review, an introduction to these new thin-film systems is given. The concept of quasicrystals and their approximants is explained for BaTiO3 - and SrTiO3 - derived OQCs and related periodic structures in these 2D oxides. In situ microscopy unravels the high-temperature formation process of OQCs on Pt(111). The dodecagonal structure is discussed regarding tiling statistics and tiling decoration based on the results of atomically resolved scanning tunneling microscopy and various diffraction techniques. In addition, angle-resolved ultraviolet photoemission spectroscopy and X-ray photoelectron spectroscopy results prove a metallic character of the 2D oxide