In this work, we present a result of PFM measurements on perforated and nonperforated Ba
0,8
Sr
0,2
TiO
3
thin epitaxial films. A huge enhancement of effective values for both lateral and vertical ...piezoelectric tensors during polarization reversal was experimentally detected. An assumption of short-range quadrant domain pattern in perforated ferroelectric structure was discussed. The obtained results are crucial for calculations of ferroelectric polarization in ferroelectric photonic crystals and metamaterials.
By means of optical pump–probe technique, the ultrafast dynamics of nonlinear optical response of the ferroelectric semiconductor Sn
2
P
2
S
6
crystal excited with a femtosecond laser pulse has been ...investigated. It has been shown that, under the action of femtosecond pulses, change in optical second harmonic generation occurs in the sample, which can be due to screening of existing electric polarization.
Temperature dependences of electric field-induced and magnetic field-induced optical second harmonic generation (SHG) were used to study La
0.7
Ca
0.25
MnO
3
/BaTiO
3
(LCMO/BTO) superlattice. Ferroic ...properties of the superlattice are reveal by magnetic field-induced and electric field-induced SHG hysteresis loops ("magnetic" and "electric" SHG loops). However, direct modifications of the SHG hysteresis loops by the other field (electric field for the "magnetic loop" and vice versa) were not found. Strong modifications of the "electric" SHG hysteresis loops occur at temperatures close to the paramagnetic-ferromagnetic and the insulator-metal phase transitions in LCMO. In this way, the magnetoelectric interaction in an LCMO/BTO superlattice was established indirectly.
The propagation of short optical and terahertz pulses through a noncentrosymmetric (ferroelectric) film on a centrosymmetric substrate is considered. The effect of terahertz electro-induced second ...harmonic generation is observed in the film. It is shown that the difference in the group velocities of THz and optical pulses leads to a non-mirror-like dependence of the transient nonlinear-optical response upon a mirror image of the film-substrate structure relative to its surface.
Electric field distribution during polarization reversal in planar geometry is studied in BaSrTiO
3
epitaxial films experimentally and numerically. Regularly perforated film forms two-dimensional ...photonic crystal, in which polarization can be reversed using interdigital electrode system. Dimensions of the system: electrode and gap width and hole depth (all of 1-2 μm) together with the electrode thickness (300 nm) reduce the spatial resolution of the used electric-force microscopy but allow nevertheless to monitor the numerically predicted sharp increase of electric field at the edges of electrode and at the holes.
Zn
1−
x
Ni
x
Fe
2
O
4
ferrites up to
x
= 1.0 with Δ
x
= 0.2 have been synthesized
via
solid state reactions and the sol-gel autocombustion technique with step-by-step co-firing. Data on the chemical ...composition and the surface morphology of the samples have been obtained using a scanning electron microscope. An X-ray powder diffractometer has been used to establish the phase purity and to determine the unit cell parameters. It has been found that the obtained samples had a spinel structure with the
Fd
3&cmb.macr;
m
(No. 227) space group. The unit cell parameters decrease with increasing nickel concentration. The
a
unit cell parameter decreases almost linearly from ∼8.443 Å for
x
= 0.0 down to ∼8.337 Å for
x
= 1.0. The
V
unit cell volume decreases almost linearly from ∼601.72 Å
3
for
x
= 0.0 down to ∼579.52 Å
3
for
x
= 1.0. The magnetic characteristics of the obtained samples are determined and discussed. The Curie point of obtained samples varies in the range of 803.5-572.7 K. The maximum spontaneous magnetization of ∼74.6 emu g
−1
at room temperature was fixed for the solid solution with
x
= 0.6. Ac-resistivity drops by more than 3 orders of magnitude in the frequency range 1-10
6
Hz. The composition with
x
= 0.6 has the minimum ac-resistivity of 5.3 kOm cm at a frequency of 10
6
Hz. The maximum value of the (
μ
′) real part of ∼11.2 and (
μ
′′) imaginary part of ∼5.2 of the permeability in the frequency range of 50 MHz-10 GHz is observed for the composition with
x
= 0.4. The composite samples for the microwave study were prepared by mixing of the ferrite powders with molten paraffin wax. The volume fraction of the ferrite filler in the composites was 25%. The largest value of the (
μ
′) real part of ∼3 and (
μ
′′) imaginary part of ∼0.63 of permeability is found for the
x
= 0.4 composite. The formation of the composite significantly reduces permeability.
Increase in the spontaneous magnetization up to
x
< 0.5 is a sequence of appearance of the additional magnetic moment of 2
μ
B
of the Ni
2+
cations in tetrahedral positions. For
x
> 0.5, the moment decreases in octahedral positions and the spontaneous magnetization also decreases.
The local piezoresponse in a Ba0.8Sr0.2TiO3 epitaxial ferroelectric film perforated by cylindrical channels has been investigated experimentally by means of piezoresponse force microscopy (PFM). A ...large enhancement of the effective values for both lateral and vertical components of piezoelectric tensor was experimentally detected in the perforated film as compared to non-perforated structure-by a factor of 8 for the lateral and by a factor 2 for the vertical piezoresponse. This result is consistent with the previously reported enhancement of the optical second harmonic generation over perforated films observed in macroscopic experiments. We assume that a possible mechanism for the increased PFM response is due to reduction of stress and clamping in the film imposed by the substrate. The obtained insight is critical for understanding nanoscale piezo- and ferroelectric responses in photonic crystals fabricated by focused ion beam milling.
The oxide heterostructure (YFeO sub(3)) sub(5)(LaFeO sub(3)) sub(5) sub(40), which is magnetically ordered and piezoelectric at room temperature, has been constructed from two weak ferromagnetic AFeO ...sub(3) perovskites with different A cations using RHEED-monitored pulsed laser deposition. The polarisation arises through the removal of inversion centres present within the individual AFeO sub(3) components. This symmetry reduction is a result of combining ordering on the A site, imposed by the periodicity of the grown structure, with appropriate orientations of the octahedral tilting characteristic of the perovskite units themselves, according to simple symmetry-controlled rules. The polarisation is robust against A site interdiffusion between the two layers which produces a sinusoidally modulated occupancy that retains the coupling of translational and point symmetries required to produce a polar structure. Magnetization and magneto-optical Kerr rotation measurements show that the heterostructure's magnetic structure is similar to that of the individual components. Evidence of the polarity was obtained from second harmonic generation and piezoelectric force microscopy measurements. Modeling of the piezoresponse allows extraction of d sub(33) (approximately 10 pC N super(-1)) of the heterostructure, which is in agreement with DFT calculations.
The ultrafast dynamics of electrons and phonons excited by femtosecond light pulses in ferroelectric semiconductor Sn
2
P
2
S
6
is investigated using the optical pump–probe technique. It is ...demonstrated that a soft mode can be excited in this ferroelectric in the vicinity of the phase transition initiated by laser radiation.
Optical second harmonic generation (SHG), which is sensitive to the symmetry breaking, provides a powerful experimental technique for investigation of ferroic materials, i.e. ferroelectrics, ...magnetics, and multiferroics. A far-field confocal microscopy provides three-dimensional imaging of an order parameter of ferroics with a spatial resolution up to diffraction limit of a probing wavelength. In this paper, we discuss general important consideration regarding SHG microscopy and show new imaging techniques for ferroelectric and magnetic domains and switching, bio-inspired ferroelectrics, as well as femtosecond laser annealed ferroelectric microstructures.
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