Papers by Keyword: Multiferroic

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Authors: C. Kanagaraj, Baskaran Natesan
Abstract: We have performed detailed structural, electronic and magnetic properties of high - TC multiferroic CuO using first principles density functional theory. The total energy results revealed that AFM is the most stable magnetic ground state of CuO. The DOS and electronic band structure calculations show that in the absence of on-site Coulomb interaction (U), AFM structure of CuO heads to a metallic state. However, upon incorporating U in the calculations, a band gap of 1.2 eV is recovered. Furthermore, the Born effective charges calculated on Cu does not show any anomalous character.This suggests that the polarization seen in CuO could be attributed to the spin induced AFM ordering effect.
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Authors: Vladimir M. Petrov, Mirza I. Bichurin, Gopalan Srinivasan, V.M. Laletin, Roman V. Petrov
Abstract: A model is discussed here for the resonance enhancement of magnetoelectric (ME) interactions in ferrite-piezoelectric bilayers at frequencies corresponding to bending oscillations. The thickness dependence of stress, strain and magnetic and electric fields within the sample are taken into account so that the bending deformations could be considered in an applied magnetic or electric field. The boundary conditions corresponding to bilayers that are free to vibrate at both ends, or simply supported at both ends, or fixed at one end are considered. The explicit expressions for ME voltage coefficients are derived by way of exact solution of electrostatic, magnetostatic and elasto-dynamic equations for thin plate and disk-shaped bilayers. The model is applied to a specific case of nickel and lead zinconate titanate (PZT) bilayer. Theoretical ME voltage coefficients versus frequency and PZT to nickel thickness ratio profiles are in excellent agreement with data.
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Authors: Chun Lin Fu, Meng Huo, Wei Cai, Xiao Ling Deng
Abstract: BiFeO3 powders were prepared by sol-gel process and calcined at different temperatures. The DTA curve shows an obvious exothermic peak near 480.5°C, the temperature close to BiFeO3 formation temperature, which is agreement with the XRD results (450°C). After calcining at 600°C for 1h, XRD spectra has the emergence of several sharp diffraction peaks, compared with the standard XRD spectrum of the crystal BiFeO3. As the calcining temperature increased, the diffraction peak intensity of the XRD spectra of BiFeO3 gradually increased and the diffraction peaks became sharply, indicating that the grain size gradually became larger. There is a clear endothermic peak near 825.1°C, which is the α phase to β phase transition from the knowledge of the phase diagram and in good agreement with the reported Curie temperature.
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Authors: Ebrahim Mostafavi, Abolghasem Ataie, Mostafa Ahmadzadeh
Abstract: Multiferroic bismuth ferrite, BiFeO3, was synthesized via conventional solid-state reaction method using Bi2O3, Fe2O3 as starting materials. Effects of Bi2O3/Fe2O3 molar ratio and calcination temperature on the phase composition, morphology and magnetic properties of produced powders were systematically studied using XRD, FESEM/EDS and VSM techniques, respectively. The results revealed that BiFeO3 phase with rhombohedral R3c structure with a mean particle size of 40 nm was formed in the sample processed with a Bi2O3/Fe2O3 molar ratio of 1:1 after calcination at 800 °C. Rietveld analysis which was applied to the x-ray diffraction data via MAUD software indicated high purity of 95%wt for the above sample. Deviation from the stoichiometric molar ratio (Bi2O3/Fe2O3: 0.9, 1.1, 1.2) yielded higher content of the intermediate phases of Bi2Fe4O9 and Bi25FeO40. FESEM studies showed that the mean particle size was increased from 40 to 62 nm by increasing calcination temperature from 800 to 850 °C. VSM results for 1:1 molar ratio samples indicated that increasing the calcination temperature from 800 to 850 °C increased saturation magnetization (Ms) from 0.087 to 0.116 emu/g and also coercive field (Hc) from 60 to 100 Oe.
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Authors: Dmitry Andreevich Maslov, Yuri Borislavovich Kudasov
Abstract: Charge ordering of nonstoichiometric LuFe2O4+δ is discussed. Properties of triangular bilayer are investigated via mean field theory with Coulomb interaction between sites. It is shown that low temperature state of bilayer has dipole moment essentially under any doping parameter. Correlation between sites in neighbor layers is estimated and dimer partially disordered antiferroelectric phase is extended for the case of nonstoichiometric samples. Competition of correlation effect with bilayer interaction and external electric field is discussed. Phase diagrams for doped specimen are presented. The results of investigation are used to clarify a significant surface impact.
375
Authors: Dinesh Shukla, Nhalil E. Rajeevan, Ravi Kumar
Abstract: The attempts to combine both the magnetic and ferroelectric properties in one material started in 1960s predominantly by the group of Smolenskii and Schmid [1. Dzyaloshinskii first presented the theory for multiferroicity in Cr2O3, which was soon experimentally confirmed by Astrov [5,. Further work on multiferroics was done by the group of Smolenskii in St. Petersburg (then Leningrad) [7, but the term multiferroic was first used by H. Schmid in 1994 [. These efforts have resulted in many fundamental observations and opened up an entirely new field of study. Schmid [ defined the multiferroics as single phase materials which simultaneously possess two or more primary ferroic properties. The term multiferroic has been expanded to include materials which exhibit any type of long range magnetic ordering, spontaneous electric polarization, and/or ferroelasticity. In the past decade, several hundreds of papers related to multiferroic materials and magnetoelectric effect have been published every year, making this topic one of the hottest areas in condensed matter physics from fundamental science as well as applications viewpoints. This article sheds light on recent progress about the developments of new multiferroics by combining unconventional magnetism and ferroelectricity with an emphasis on Bi based multiferroic materials. Specifically results of Ti doped BiMn2O5 and Bi doped Co2MnO4 multiferroics are discussed.
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Authors: Shigeki Sawamura, Naonori Sakamoto, De Sheng Fu, Kazuo Shinozaki, Hisao Suzuki, Naoki Wakiya
Abstract: Thermal stability of bottom electrode thin films (La0.5Sr0.5)CoO3 (LSCO) and (La0.6Sr0.4)MnO3 (LSMO) were investigated. The crystallization and surface morphology of the heterostructure were characterized using x-ray diffraction and atomic force microscopy. Resistivity of the LSCO thin film was 25 cm. However, the resistivity of LSCO thin film increases sharply with annealing temperature. The LSMO thin film has high resistivity (100 mcm). The film does not decompose after thermal processing at 900 °C. To confirm thermal stability, we examined the effect of post annealing at various temperatures on the morphology and resistivity. Results showed that LSMO has higher thermal stability than that of LSCO.
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Authors: V.A. Khomchenko, Michael Kopcewicz, Armandina M. Lima Lopes, Yuri G. Pogorelov, J.P. Araujo, Joaquim M. Vieira, Andréi L. Kholkin
Abstract: Investigation of crystal structure and magnetic properties of the diamagnetically- substituted Bi1-xAxFeO3-x/2 (A= Ca, Sr, Pb, Ba; x= 0.2, 0.3) polycrystalline samples has been carried out. It has been shown that the heterovalent A2+ substitution result in the formation of oxygen vacancies in the host lattice. The solid solutions have been found to possess a rhombohedrally distorted perovskite structure described by the space group R3c. Magnetization measurements have shown that the magnetic state of these compounds is determined by the ionic radius of the substituting elements. A-site substitution with the biggest ionic radius ions has been found to suppress the spiral spin structure of BiFeO3 giving rise to the appearance of weak ferromagnetism.
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Authors: Alexander P. Nosov, Mikhail A. Semkin, A.E. Teplykh, S.G. Bogdanov, Natali V. Urusova, Yu.N. Skryabin, Alexander N. Pirogov, Victor G. Vasiliev, Elena V. Vladimirova, Tatyana S. Karpova
Abstract: Multiferroic composites of (x)NiFe2O4 + (1-x)BaTiO3 with x = 0.2, 0.3 and 0.4 and (x)CoFe2O4 + (1-x)BaTiO3 with x = 0.2, and 0.4 have been synthesized by mixing NiFe2O4 (CoFe2O4) spinel and BaTiO3 piezoelectric. Distribution of Ni (Co) ions on 8a and 16d positions of spinel lattice (space group F d-3m) is determined by neutron powder diffraction. Wave vector of magnetic structure of the spinel is k = 0. The dielectric permittivity of the composites was measured for the frequency range 102 – 105 Hz. At low frequencies the dielectric permittivity decreased from ~940 for x = 0.2 to ~360 for 0.4.
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Authors: Seong Su Lee, Mikhail A. Semkin, Alexander N. Pirogov
Abstract: Neutron diffraction has been carried out to study temperature evolution of crystal and magnetic structure parameters of the multiferroic (0.9)BiFeO3 + (0.1)BaTiO3 over region (300 – 1000) K. Crystal structure is rhombohedral over whole temperature region and it is described by the R3c space group. The lattice parameters increase with temperature. The Ba ions are placed in the Bi sublattice and the Ti ions partly occupy the Fe sublattice. Assuming that the sample has a modulated magnetic structure with the propagation vector k = [0.0045, 0.0045, 0], we obtained a temperature dependence of the Fe-ion magnetic moment. The value of the moment is equaled to be μ = (3.46 ± 0.05) μB at 300 K and becomes zero at 600 K.
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