167 research outputs found
Interfacial effects on the polarization of films
By considering an interfacial layer between the electrode and the
() layer, the polarization and the hysteresis behavior of
film are simulated. It is found that the non-ferroelectric interface will
increase the coercive field, and remarkably suppress the polarization of the
ultrathin film under low applied fields. Due to the competition between the
interfacial effect and the internal compressive stress, the maximum
polarization on the P-E loop of a film can be independent on the film
thickness under an adequate applied field.Comment: 3 pages, 2 figure
Ultrafast luminescence of Ga- and In-doped ZnO ceramics
The work of authors (a-c) was financially supported by Russian Foundation for Basic Research (RFBR, Russia) and the work of the last author (d) had financial support from State Education Development Agency (VIAA, Latvia) . All of that was approved as a result of ERA.Net RUS PLUS 2017 joint call for proposals. Here is the link for the joint call for reference: https://www.eranet-rus.eu/en/196.php .In the presented work we compare luminescence characteristics of ZnO:Ga and ZnO:In ceramics prepared by hot uniaxial pressing method. Two types of initial powders were used. The first one was nanosized powder prepared by precipitation method. In the second case we used microsized powders and mechanical admixturing the oxides of intended dopant. In both cases doping by the trivalent ions lead to a significant quenching of ZnO visible emission and an increase in near-band-edge luminescence. The study has shown that the type of dopant greatly affects the transmittance of ceramics prepared from nano- and micro sized powders. Several reasons for the specific effect of powder preparation process and a type of introduced dopant, including changes in dopant solubility, their interaction with the grain boundaries, etc., were considered. © 2021 The Author(s). Published under the CC-BY-NC-ND license.Russian Foundation for Basic Research (RFBR, Russia); State Education Development Agency (VIAA, Latvia); ERA.Net RUS PLUS 2017 joint call for proposals; Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Unionâs Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2
Electromagnon excitations in modulated multiferroics
The phenomenological theory of ferroelectricity in spiral magnets presented
in [M. Mostovoy, Phys. Rev. Lett. 96, 067601 (2006)] is generalized to describe
consistently states with both uniform and modulated-in-space ferroelectric
polarizations. A key point in this description is the symmetric part of the
magnetoelectric coupling since, although being irrelevant for the uniform
component, it plays an essential role for the non-uniform part of the
polarization. We illustrate this importance in generic examples of modulated
magnetic systems: longitudinal and transverse spin-density wave states and
planar cycloidal phase. We show that even in the cases with no uniform
ferroelectricity induced, polarization correlation functions follow to the soft
magnetic behavior of the system due to the magnetoelectric effect. Our results
can be easily generalized for more complicated types of magnetic ordering, and
the applications may concern various natural and artificial systems in
condensed matter physics (e.g., magnon properties could be extracted from
dynamic dielectric response measurements).Comment: 5 page
Multiferroics: different ways to combine magnetism and ferroelectricity
Multiferroics - materials which are simultaneously (ferro)magnetic and
ferroelectric, and often also ferroelastic, attract now considerable attention,
both because of the interesting physics involved and as they promise important
practical applications. In this paper I give a survey of microscopic factors
determining the coexistence of these properties, and discuss different possible
routes to combine them in one material. In particular the role of the
occupation of d-states in transition metal perovskites is discussed, possible
role of spiral magnetic structures is stressed and the novel mechanism of
ferroelectricity in magnetic systems due to combination of site-centred and
bond-centred charge ordering is presented. Microscopic nature of multiferroic
behaviour in several particular materials, including magnetite Fe3O4, is
discussed.Comment: to be published as a Topical Review in Journ.Magn.Magn.Mate
Effect of Yb3+ doping level on the structure and spectroscopic properties of ZnO optical ceramics
This work was partly supported by the RFBR (Grant 19-03-00855).Zinc oxide optical ceramics with hexagonal structure doped with 0.6 â5.0 wt% Yb were fabricated by uniaxial hot pressing of commercial oxide powders at 1180 °C in vacuum. The ceramics were characterized by X-ray diffraction, SEM, EDX, X-ray and optical spectroscopy. It is shown that Yb3+ ions are distributed between C-type Yb2O3 sesquioxide crystals and ZnO grain boundaries. The Yb3+ doping of ZnO ceramics enhances the near-band-edge emission of zinc oxide. ZnO:Yb optical ceramics are promising for optoelectronic applications. © 2021 Institute of Physics Publishing. All rights reserved.RFBR (Grant 19-03-00855); The Institute of Solid State Physics, University of Latvia (Latvia), as the Centre of Excellence has received funding from the European Unionâs Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-Teaming Phase2 under grant agreement No. 739508, project CAMART2
Electric-field-induced spin-flop in BiFeO3 single crystals at room-temperature
Bismuth ferrite, BiFeO3, is the only known room-temperature 'multiferroic'
material. We demonstrate here, using neutron scattering measurements in high
quality single crystals, that the antiferromagnetic and ferroelectric orders
are intimately coupled. Initially in a single ferroelectric state, our crystals
have a canted antiferromagnetic structure describing a unique cycloid. Under
electrical poling, polarisation re-orientation induces a spin flop. We argue
here that the coupling between the two orders may be stronger in the bulk than
that observed in thin films where the cycloid is absent
Structural, optical, and luminescence properties of ZnO:Ga optical scintillation ceramic
This paper discusses the characteristics of ZnO and ZnO:Ga ceramics fabricated by uniaxial hot pressing. The short-wavelength transmission limit of zinc oxide ceramics is in the 370-nm region; the long-wavelength limit is determined by the free-charge-carrier concentration and lies in the interval from 5 to 9 ÎŒm. The total transmittance of such ceramics in the visible and near-IR regions is about 70% when the sample is 0.5 mm thick. The luminescence spectrum is represented by a broad emission band with maximum at 580 nm, having a defect nature. The introduction of 0.03â0.1 mass % gallium into the zinc oxide structure inhibits grain growth and increases the free-charge-carrier concentration to 3.44 Ă 1019 cmâ3. As the gallium concentration increases in the range 0.05â0.1 mass % in a ceramic of composition ZnO:Ga, the defect luminescence band is suppressed and a characteristic exciton luminescence is formed with a maximum corresponding to 389 nm and a damping time constant of 1.1 ns.Russian Foundation for Basic Research (RFBR) (18-52-76002); Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Unionâs Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART
Origin of magnetoelectric behavior in BiFeO
The magnetoelectric behavior of BiFeO has been explored on the basis of
accurate density functional calculations. The structural, electronic, magnetic,
and ferroelectric properties of BiFeO are predicted correctly without
including strong correlation effect in the calculation. Moreover, the
experimentally-observed elongation of cubic perovskite-like lattice along the
[111] direction is correctly reproduced. At high pressure we predicted a
pressure-induced structural transition and the total energy calculations at
expanded lattice show two lower energy ferroelectric phases, closer in energy
to the ground state phase. Band-structure calculations show that BiFeO will
be an insulator in A- and G-type antiferromagnetic phases and a metal in other
magnetic configurations. Chemical bonding in BiFeO has been analyzed using
various tools and electron localization function analysis shows that
stereochemically active lone-pair electrons at the Bi sites are responsible for
displacements of the Bi atoms from the centro-symmetric to the
noncentrosymmetric structure and hence the ferroelectricity. A large
ferroelectric polarization (88.7 C/cm) is predicted in accordance
with recent experimental findings. The net polarization is found to mainly (
98%) originate from Bi atoms. Moreover the large scatter in experimentally
reported polarization values is due to the large anisotropy in the spontaneous
polarization.Comment: 19 pages, 12 figures, 4 table
Low Symmetry Phase in (001) BiFeO Epitaxial Constrained Thin Films
The lattice of (001)-oriented BiFeO epitaxial thin film has been
identified by synchrotron x-ray diffraction. By choosing proper scattering
zones containing the fixed (001) reflection, we have shown that low-symmetry
phases similar to a phase exist in the thin film at room temperature.
These results demonstrate a change in phase stability from rhombohedral in bulk
single crystals, to a modified monoclinic structure in epitaxial thin films
Preparation, structural, dielectric and magnetic properties of LaFeO3-PbTiO3 solid solutions
Solid solutions of (1-x)LaFeO3-(x)PbTiO3 (0<x<1) have been prepared by
conventional solid-state reaction. These complex perovskites have been studied
by means of X-ray (XRPD) and neutron powder (NPD) diffraction, complemented
with dielectric, magnetic, heat capacity and M\"ossbauer measurements. Complete
solubility in the perovskite series was demonstrated. The NPD and XRPD patterns
were successfully refined as orthorhombic (x \leq 0.7) and tetragonal (x \geq
0.8). A composition-driven phase transformation occurs within the interval
0.7<x<0.8. The samples with x<0.5 showed evidence of long-range magnetic
ordering with an G-type antiferromagnetic arrangement of the magnetic moments
of the Fe3+ cations in the B-site with propagation vector k = (0,0,0). Based on
the obtained experimental data, a combined structural and magnetic phase
diagram has been constructed. The factors governing the structural, dielectric
and magnetic properties of (1-x) LaFeO3 - (x)PbTiO3 solid solutions are
discussed, as well as their possible multiferroicity.Comment: 33 pages, 15 figure
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