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ABSTRACT: BiFeO3 thin oriented films are grown on SrTiO3(001) and ZrO2(Y2O3)(001) substrates by metalloorganic chemical vapor deposition (MOCVD) in the temperature range T= 500–800°C. Iron dipivaloylmethanate Fe(thd)3 and triphenylbismuth Bi(C6H5)3 are used as volatile precursors. It is shown that the high thermal stability of Bi(C6H5)3 leads to significant deviations of the Bi: Fe ratio in the film from their ratio in the precursor flow. An increase in the
residence time of the precursor flow in the reactor makes this ratio close to unity. The film-substrate epitaxial relations
are determined. It is found that the film orientation on the ZrO2(Y2O3)(001) substrate changes with increasing temperature. Optical second harmonic generation (SHG) measurements show the presence
of ferroelectric ordering in the films. A significant decrease in the Curie temperature due to epitaxial stress is found.
At the same time, the magnetization noticeably increases as compared to a BiFeO3 single crystal.
Journal of Surface Investigation X-ray Synchrotron and Neutron Techniques 04/2012; 2(1):1-11. · 0.34 Impact Factor
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ABSTRACT: The results of structural neutron experiments on determining crystal and magnetic phase states of perovskite-like manganites
R0.5Sr0.5MnO3 (R = 152Sm, Nd0.772Tb0.228, and Nd0.544Tb0.456) are reported. Experiments are carried out for revealing microscopic factors responsible for the giant oxygen isotope effect
that was discovered recently in Sm1−x
Sr
x
MnO3 for x ≈ 0.5. It is shown that separation into two crystal phases P
1 and P
2 with the same spatial symmetry but different types of Jahn-Teller distortions in MnO6 octahedra and magnetic ordering of Mn atoms takes place in all studied compounds at low temperatures. Structural analysis
has been carried out successfully owing to exceptionally large differences in the unit cell parameters of the coexisting phases.
The P
1 phase is ferromagnetic and MnO6 octahedra are distorted only slightly. The P
2 phase is antiferromagnetic (A-type ordering) and MnO6 octahedra are strongly compressed in the apical direction. The relative volumes occupied by the P
1 and P
2 phases depend on the mean radius of the A cation, and the replacement of 16O by 18O results in their redistribution in favor of the P
2 phase. The results unambiguously point to the percolation nature of the metal-insulator transition in a Sm-containing compound
upon isotopic substitution of oxygen due to a sharp decrease (from 65 to 13%) in the fraction of ferromagnetic phase P
1. In all investigated compounds, the ordered magnetic moment of manganese Mn in the P
1 and P
2 phases varies from 1.7μB to 3.5μB. The data on the evolution of the miscrostructure parameters during a phase transition to the stratified state indicate that
the initial spread in the A cation radii, as well as the internal microstrains, produce a critical effect on the formation of mesoscopic phase separation.
Journal of Experimental and Theoretical Physics 04/2012; 106(3):528-541. · 1.03 Impact Factor
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ABSTRACT: Sm0.55Sr0.45MnO3/Nd0.55Sr0.45MnO3 heterostructure consisting of layers with different Curie temperatures is studied. By comparing data for IR transmission,
resistivity, magnetotransmission, magnetoresistance, and Kerr effect measured on the side of the film and substrate, the Curie
temperatures of the layers are determined and the contributions of the layers to the magnetoresistance and magnetotransmission
are estimated. A weak temperature dependence of the magnetotransmission and magnetoresistance makes manganites with a colossal
magnetoresistance and magnetotransmission candidate materials for devices without temperature stabilization.
Technical Physics 01/2008; 53(6):716-721. · 0.50 Impact Factor
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ABSTRACT: Optical second-harmonic generation (SHG) was applied to study the ferroelectric and magnetic properties of strained epitaxial BiFeO3 films deposited on (001) SrTiO3 substrates by metal organic chemical vapor deposition. A strong interplay between the ferroelectric and magnetic subsystems of bismuth ferrite films results in the pronounced temperature dependence of the SHG intensity. The decrease of the critical temperature of the ferroelectric phase transition and the expansion of the nonlinear transient area near Néel temperature were observed for the strained BiFeO3 films.
Journal of Materials Research. 07/2007; 22(08):2063 - 2067.
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ABSTRACT: Results of neutron diffraction studies of R0.5Sr0.5MnO3 manganites (R = Sm, Nd0.772Tb0.228, and Nd0.544Tb0.456) performed to reveal the microscopic origins of the giant oxygen isotope effect recently discovered in Sm0.5Sr0.5MnO3 are presented. It is shown that two crystalline phases differing in the type of Jahn-Teller distortions of oxygen octahedra
and in the type of magnetic ordering coexist at low temperatures in all the studied compositions. A scenario for the observed
phase transitions is suggested based on the diffraction data. It is found that the percolation transition from the metallic
to insulating state in compositions with Sm upon substitution of 18O for 16O is associated with a sharp (from 65 to 13%) decrease in the volume of the ferromagnetic metallic phase.
JETP Letters 01/2005; 82(9):594-598. · 1.35 Impact Factor
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ABSTRACT: The measurements of temperature dependence of electrical resistivity ρ(T) and magnetic susceptibility χ(T) as well as neutron diffraction studies were performed for three groups of R1-xSrxMnO3 manganites. Each group was characterized by the same average ionic radius 〈rA〉 of rare earth R, but by different degree of cation disorder . For each composition, the isotope-substituted samples () were also prepared. It was shown that the increase in σ2 at fixed 〈rA〉 leads to appreciable changes in electrical and magnetic properties, as well as to a more pronounced isotope effect. Large values of σ2 give rise to a significant scatter in the values of the electron hopping integral for neighboring Mn sites. This favors the electron localization and the tendency to antiferromagnetism in the phase-separated state, thus enhancing the effect of oxygen isotope substitution.
Journal of Magnetism and Magnetic Materials 300(1). · 1.78 Impact Factor
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ABSTRACT: BiFeO3 thin films were grown on (001) SrTiO3 and (001) ZrO2(Y2O3) substrates by single source metalorganic chemical vapor deposition in the temperature range T = 500 ÷ 800 °C using Fe(thd)3 and Bi(C6H5)3 as volatile precursors. X-ray diffraction analysis shows cube-on-cube epitaxial growth of BiFeO3 on (001) SrTiO3. The strongly reduced bismuth transfer into the film due to the high thermal stability of Bi(C6H5)3 was counterbalanced by the increase of the total pressure as well as of the residence time of the precursor flow in the reactor; the Bi/Fe ratio in the film thus becomes close to that in the precursor mixture. Optical second harmonic generation measurements have evidenced the ferroelectric ordering in BiFeO3 films and the apparent decrease of the Curie temperature of the strained films as compared to BiFeO3 single crystal.
Thin Solid Films 515(16):6416-6421. · 1.89 Impact Factor
