Temperature-Driven Transformation of the Crystal and Magnetic Structures of BiFeMnO Ceramics.

The compound BiFeMnO consisting at room temperature of coexistent anti-polar orthorhombic and polar rhombohedral phases has a metastable structural state, which has been studied by laboratory X-ray, synchrotron and neutron diffraction, magnetometry, differential thermal analysis, and differential scanning calorimetry. Thermal annealing of the sample at temperatures above the temperature-driven phase transition into the single phase rhombohedral structure (~700 K) causes an increase of the volume fraction of the rhombohedral phase at room temperature from ~10% up to ~30%, which is accompanied by the modification of the magnetic state, leading to strengthening of a ferromagnetic component. A strong external magnetic field (~5 T) applied to the sample notably changes its magnetic properties, as well as provides a reinforcement of the ferromagnetic component, thus leading to an interaction between two magnetic subsystems formed by the antiferromagnetic matrix with non-collinear alignment of magnetic moments and the nanoscale ferromagnetic clusters coexisting within it.

Structural and Magnetic Phase Transitions in BiFeMnO Solid Solution Driven by Temperature.

The crystal structure and magnetic state of the (1 − x)BiFeO3-(x)BiMnO3 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 < x1 < 0.

Crystal Structure and Concentration-Driven Phase Transitions in LuScFeO (0 ≤ ≤ 1) Prepared by the Sol-Gel Method.

The structural state and crystal structure of LuScFeO (0 ≤ ≤ 1) compounds prepared by a chemical route based on a modified sol-gel method were investigated using X-ray diffraction, Raman spectroscopy, as well as scanning electron microscopy. It was observed that chemical doping with Sc ions led to a structural phase transition from the orthorhombic structure to the hexagonal structure via a wide two-phase concentration region of 0.1 < < 0.

Exploring Charged Defects in Ferroelectrics by the Switching Spectroscopy Piezoresponse Force Microscopy.

Monitoring the charged defect concentration at the nanoscale is of critical importance for both the fundamental science and applications of ferroelectrics. However, up-to-date, high-resolution study methods for the investigation of structural defects, such as transmission electron microscopy, X-ray tomography, etc., are expensive and demand complicated sample preparation.

Crystal and Magnetic Structure Transitions in BiMnO 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 () to another monoclinic (), and then to the orthorhombic () 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.

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.

A Facile Synthesis and Characterization of Highly Crystalline Submicro-Sized BiFeO.

In this study, a highly crystalline bismuth ferrite (BFO) powder was synthesized using a novel, very simple, and cost-effective synthetic approach. It was demonstrated that the optimal annealing temperature for the preparation of highly-pure BFO is 650 °C. At lower or higher temperatures, the formation of neighboring crystal phases was observed.

Investigation of Local Conduction Mechanisms in Ca and Ti-Doped BiFeO Using Scanning Probe Microscopy Approach.

In this work we demonstrate the role of grain boundaries and domain walls in the local transport properties of n- and p-doped bismuth ferrites, including the influence of these singularities on the space charge imbalance of the energy band structure. This is mainly due to the charge accumulation at domain walls, which is recognized as the main mechanism responsible for the electrical conductivity in polar thin films and single crystals, while there is an obvious gap in the understanding of the precise mechanism of conductivity in ferroelectric ceramics. The conductivity of the BiCaFeTiO (x = 0, 0.

Peculiarities of the Crystal Structure Evolution of BiFeO-BaTiO Ceramics across Structural Phase Transitions.

Evolution of the crystal structure of ceramics BiFeO-BaTiO across the morphotropic phase boundary was analyzed using the results of macroscopic measuring techniques such as X-ray diffraction, differential scanning calorimetry, and differential thermal analysis, as well as the data obtained by local scale methods of scanning probe microscopy. The obtained results allowed to specify the concentration and temperature regions of the single phase and phase coexistent regions as well as to clarify a modification of the structural parameters across the rhombohedral-cubic phase boundary. The structural data show unexpected strengthening of structural distortion specific for the rhombohedral phase, which occurs upon dopant concentration and temperature-driven phase transitions to the cubic phase.

Magnetic Properties of LaAMnO (A: Li, Na, K) Nanopowders and Nanoceramics.

Nanocrystalline LaAMnO (where A is Li, Na, K) powders were synthesized by a combustion method. The powders used to prepare nanoceramics were fabricated via a high-temperature sintering method. The structure and morphology of all compounds were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM).

Functional Magnetic Composites Based on Hexaferrites: Correlation of the Composition, Magnetic and High-Frequency Properties.

The paper describes preparation features of functional composites based on ferrites, such as "Ba(FeGa)O/epoxy," and the results of studying their systems; namely, the correlation between structure, magnetic properties and electromagnetic absorption characteristics. We demonstrated the strong mutual influence of the chemical compositions of magnetic fillers (Ba(FeGa)O 0.01 < < 0.

Ferromagnetic-like behavior of BiLaFeO-KBr nanocomposites.

We studied magnetostatic response of the BiLaFeO- KBr composites (BLFO-KBr) consisting of nanosized (≈100 nm) ferrite BiLaFeO (BLFO) conjugated with fine grinded ionic conducting KBr. When the fraction of KBr is rather small (less than 15 wt%) the magnetic response of the composite is very weak and similar to that observed for the BLFO (pure KBr matrix without BiLaFeO has no magnetic response as anticipated). However, when the fraction of KBr increases above 15%, 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.

Molecular modeling of the piezoelectric properties of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene or graphene oxide.

Molecular modeling of ferroelectric composites containing polyvinylidene fluoride (PVDF) and either graphene (G) or graphene oxide (GO) were performed using the semi-empirical quantum approximation PM3 in HyperChem. The piezo properties of the composites were analyzed and compared with experimental data obtained for P(VDF-TrFE)-GO films. Qualitative agreement was obtained between the results of the modeling and the experimental results in terms of the properties of the measured effective piezoelectric coefficient d and its decrease in the presence of G/GO in comparison with the average computed piezoelectric coefficient .

Novel multiferroic state and ME enhancement by breaking the AFM frustration in LuMnO.

This study provides a comprehensive insight into the effects of controlled off-stoichiometry on the structural and multiferroic properties of the hexagonal manganite LuMnO (x = 0.02; δ ∼ 0), supported by neutron powder diffraction measurements confirming single phase P6cm symmetry and evidencing a relevant ferromagnetic component, below T ∼ 90 K, which breaks the archetypal geometrically frustrated antiferromagnetic state typically ascribed to LuMnO. The perturbations in the triangular disposition of spins prompt an additional electric polarization contribution and a clear enhancement of the magnetoelectric coupling which are in good agreement with the results of first principles calculations.

Breaking the geometric magnetic frustration in controlled off-stoichiometric LuMn1+zO3+δ compounds.

This study explores controlled off-stoichiometric LuMn1+zO3+δ (|z| < 0.1) compounds, intended to retain the utter LuMnO3 intrinsic hexagonal symmetry and ferroelectric properties. X-ray powder diffraction measurements evidenced a single phase P63cm structure.

Ferromagnetic interactions in Mn3+ based perovskites.

La0.7Sr0.3Mn(3+)0.

Magnetic and structural phase transitions in La0.5Sr0.5CoO(3-δ) (0 ≤ δ < 0.3) cobaltites.

The evolution of the crystal structure and the magnetic properties was investigated in the La0.5Sr0.5CoO(3-δ) (0 < δ < 0.