32 research outputs found
Fixed Volume Effect on Polar Properties and Phase Diagrams of Ferroelectric Semi-ellipsoidal Nanoparticles
For advanced applications in modern industry it is very important to reduce
the volume of ferroelectric nanoparticles without serious deterioration of
their polar properties. In many practically important cases fixed volume
(rather than fixed size) corresponds to realistic technological conditions of
nanoparticles fabrication. The letter is focused on the theoretical study of
the behavior of ferroelectric polarization, paramagnetoelectric coefficient and
phase diagrams of semi-ellipsoidal nanoparticles with fixed volume V. Our
approach combines the Landau-Ginzburg-Devonshire phenomenology, classical
electrostatics and elasticity theory. Our results show that the size effects of
the phase diagrams and polarization of semi-ellipsoidal BiFeO3 nanoparticles
nontrivially depends on V. These findings provide a path to optimize the polar
properties of nanoparticles by controlling their phase diagrams at a fixed
volume.Comment: 15 pages, 5 figures, we added the section IV. Paramagnetoelectric
(PME) coefficient at fixed volume in this version and changed title and
abstract accordingl
Mesoscopic theory of defect ordering-disordering transitions in thin oxide films
Ordering of mobile defects in functional materials can give rise to
fundamentally new phases possessing ferroic and multiferroic functionalities.
Here we develop the Landau theory for strain induced ordering of defects (e.g.
oxygen vacancies) in thin oxide films, considering both the ordering and
wavelength of possible instabilities. Using derived analytical expressions for
the energies of various defect-ordered states, we calculated and analyzed phase
diagrams dependence on the film-substrate mismatch strain, concentration of
defects, and Vegard coefficients. Obtained results open possibilities to create
and control superstructures of ordered defects in thin oxide films by selecting
the appropriate substrate and defect concentration.Comment: 30 pages, 5 figures, 1 appendi
Structural and Magnetic Phase Transitions in BiFeMnO Solid Solution Driven by Temperature
The crystal structure and magnetic state of the (1 − x)BiFeO-(x)BiMnO solid solution has been analyzed by X-ray diffraction using lab-based and synchrotron radiation facilities, magnetization measurements, differential thermal analysis, and differential scanning calorimetry. Dopant concentration increases lead to the room-temperature structural transitions from the polar-active rhombohedral phase to the antipolar orthorhombic phase, and then to the monoclinic phase accompanied by the formation of two-phase regions consisting of the adjacent structural phases in the concentration ranges 0.25 < x < 0.30 and 0.50 ≤ x < 0.65, respectively. The accompanied changes in the magnetic structure refer to the magnetic transitions from the modulated antiferromagnetic structure to the non-colinear antiferromagnetic structure, and then to the orbitally ordered ferromagnetic structure. The compounds with a two-phase structural state at room temperature are characterized by irreversible temperature-driven structural transitions, which favor the stabilization of high-temperature structural phases. The magnetic structure of the compounds also exhibits an irreversible temperature-induced transition, resulting in an increase of the contribution from the magnetic phase associated with the high-temperature structural phase. The relationship between the structural parameters and the magnetic state of the compounds with a metastable structure is studied and discussed depending on the chemical composition and heating prehistory
Crystal and magnetic structure transitions in bimno3+δ ceramics driven by cation vacancies and temperature
The crystal structure of BiMnO ceramics has been studied as a function of nominal oxygen excess and temperature using synchrotron and neutron powder diffraction, magnetometry and differential scanning calorimetry. Increase in oxygen excess leads to the structural transformations from the monoclinic structure (C2/c) to another monoclinic (P2/c), and then to the orthorhombic (Pnma) structure through the two-phase regions. The sequence of the structural transformations is accompanied by a modification of the orbital ordering followed by its disruption. Modification of the orbital order leads to a rearrangement of the magnetic structure of the compounds from the long-range ferromagnetic to a mixed magnetic state with antiferromagnetic clusters coexistent in a ferromagnetic matrix followed by a frustration of the long-range magnetic order. Temperature increase causes the structural transition to the nonpolar orthorhombic phase regardless of the structural state at room temperature; the orbital order is destroyed in compounds BiMnO (δ ≤ 0.14) at temperatures above 470 °C
Ferromagnetic-like behavior of Bi0.9La0.1FeO3-KBr nanocomposites
We studied magnetostatic response of the Bi0.9La0.1FeO3-KBr composites
(BLFO-KBr) consisting of nanosized (about 100 nm) ferrite Bi0.9La0.1FeO3 (BLFO)
conjugated with fine grinded ionic conducting KBr. When the fraction of KBr is
rather small (less than 15 wt percent) the magnetic response of the composite
is very weak and similar to that observed for the BLFO (pure KBr matrix without
Bi1-xLaxFeO3 has no magnetic response as anticipated). However, when the
fraction of KBr increases above 15percent, the magnetic response of the
composite changes substantially and the field dependence of magnetization
reveals ferromagnetic-like hysteresis loop with a remanent magnetization about
0.14 emu/g and coercive field about 1.8 Tesla (at room temperature). Nothing
similar to the ferromagnetic-like hysteresis loop can be observed in BLFO
ceramics, which magnetization quasi linearly increases with magnetic field.
Different physical mechanisms were considered to explain the unusual
experimental results for BLFO-KBr nanocomposites, but only those among them,
which are highly sensitive to the interaction of antiferromagnetic
Bi0.9La0.1FeO3 with ionic conductor KBr, can be relevant. An appropriate
mechanism turned out to be ferro-magneto-ionic coupling.Comment: 24 pages, 4 figures in the main text, and supplement with 4 figure