FeBO3 Crystals Research Articles

COMPLEX OF LABORATORY GROWTH FACILITIES FOR SOLUTION–MELT SYNTHESIS CRYSTALS OF IRON BORATE FeBO3 AND CRYSTALS OF SOLID SOLUTIONS ON ITS BASIS

A complex of laboratory growth facilities, designed for solution–melt synthesis of highly perfect single crystals of iron borate, as well as crystals based on this compound, has been developed and constructed. Equipping growth plants with program-controlled functional units makes it possible to fully automate the technological process. As a result of test experiments single crystals of iron borate FeBO3 and single crystals doped with diamagnetic gallium atoms, Fe1-xGaxBO3, were obtained. The high structural perfection of the synthesized samples was confirmed by X-ray diffraction analysis and high-resolution electron microscopy.

The Evolution of the Magnetic Properties of Iron Borate Single Crystals Doped with Gallium

Highly perfect FeBO3 and Fe0.91Ga0.09BO3 single crystals were studied in a wide temperature range using SQUID magnetometry. A theoretical model describing the temperature and field dependences of the magnetization of single crystals has been developed. It is found that even a small concentration of gallium,which is a diamagnetic impurity, substantially affects the magnetic properties of single FeBO3 crystals. In par-ticular, the Fe0.91Ga0.09BO3 crystal differs from the pure FeBO3 phase in by a lower magnetic phase transition temperature and a higher antiferromagnetic susceptibility at low temperatures.

Birefringence-Mediated Enhancement of the Magneto-Optical Activity in Anisotropic Magnetic Crystals

Optical anisotropy is usually treated as an unfavorable condition for the magneto-optical measurements since it is known to diminish the Faraday rotation concerning the case of the isotropic medium. Here we show that the situation could be quite opposite: a phenomenon of birefringence-mediated enhancement of the magneto-optical activity appears if the incident light polarization and angle of incidence are set properly. The present study relies on the experimental, analytical, and numerical studies of iron borate FeBO3 crystals. We demonstrate a significant increase of the magneto-optical activity resulting in nearly 100% magneto-optical light modulation magnitude. The approach applies to other types of birefringent crystals with the magneto-optical response that makes it crucial for various practical applications, including magneto-optical microscopy, pump-probe studies, and others.

Magnetic and electric hyperfine parameters of antiferromagnet FеBO3 intended for monochromatization of synchrotron radiation

In this work, Mössbauer spectroscopy and X-ray diffraction were used to determine the precision values of the hyperfine interaction parameters and the crystal structure of FeBO3 single crystals in a wide temperature range, including the region of magnetic phase transitions (TN). A theoretical model has been developed to describe nuclear resonance transitions in iron atoms in the approximation of a combined magnetic dipole and electric quadrupole hyperfine interaction. A technique for correcting the Mössbauer spectra, considering the effective thickness of the absorber, has also been elaborated.It is shown that the appearance of two additional resonance lines in the hyperfine structure significantly affects the shape of the FeBO3 spectra near the N é el temperature (ТN). The characteristic Debye temperatures for Fe and B cations in the iron borate structure have been determined. The developed technique and the results obtained are extremely important for the use of FeBO3 crystals in new high-tech branches of science and technology, including optoelectronics and synchrotron technologies.

Formation of New Crystalline Phases upon High-Temperature Annealing of Iron Borate FeBO3 in Different Gas Media

Iron borate FeBO3 crystals are annealed in neutral, oxidizing, and reducing gas media on a specially designed setup. The effect of the chemical medium and annealing modes on the surface morphology and phase composition of the samples is established. It is shown that annealing in a neutral or oxidizing medium leads to the recrystallization of FeBO3 into the hematite α-Fe2O3 phase, whereas annealing in a reducing medium results in the formation of the pyroborate Fe2B2O5 phase and the metal α-Fe iron phase. The difference in the nature of structural transformations is associated with the change in the valence state of iron ions upon annealing in the reducing atmosphere. This result is of interest as a method for the transformation of crystalline phases.

Weak Ferromagnetism along the Triad Axis and the Basal Anisotropy Caused by the Dzyaloshinskii–Moriya Interaction and the Cubic Electric Field of the FeBO3 Crystal

Based on the spin Hamiltonian and taking into account the cubic invariant of the crystal field and the Dzyaloshinskii–Moriya interaction, the weak ferromagnetic moment along the triad axis and the basal anisotropy of FeBO3 crystals are calculated in the approximation of second-order perturbation theory.

Development of a Synthesis Technique and Characterization of High-Quality Iron Borate FeBO3 Single Crystals for Applications in Synchrotron Technologies of a New Generation

A flux growth technique for synthesizing FeBO3 single crystals of high structural perfection was developed. The high structural quality of the synthesized FeBO3 crystals was confirmed by means of double-crystal X-ray diffraction analysis both in Laue and Bragg geometries. The diffraction rocking curves taken locally and integrally over the surface are in excellent agreement with the calculated curves. Some macrodefects were revealed by X-ray topography in the crystal volume. However, the local defects do not prevent the use of defect-free regions of the crystal for synchrotron Mossbauer experiments.

Weak ferromagnetism along the third-order axis of the FeBO3 crystals caused by Fe2+ impurity ions

Using the single-ion approximation, the weak ferromagnetic moment σZ(Fe2+) along the third-order axis of FeBO3 crystals, which is caused by the contribution of Fe2+ ions, has been investigated in the framework of the model Fe2+ impurity ion –BO3 vacancy. The extreme low-temperature behavior of the total magnetic moment due to the strong dependence of the Fe2+ion contribution is predicted.

X-ray diffraction investigations of the thermal expansion of iron borate FeBO3 crystals

The lattice parameters a, c of iron borate FeBO3 polycrystals have been measured in the temperature range 25–600°C by the X-ray diffraction method. The thermal expansion coefficients α are calculated from the measured values of the parameters. A substantial anisotropy of the thermal expansion is found. It is shown that the thermal expansion coefficient αc along the c axis is greater than the thermal expansion coefficient αa in a plane perpendicular to this axis. By X-ray peak profile analysisthe crystallite size was estimated from Scherrer’s formula. We have also investigated the temperature dependence of crystallite size in FeBO3.

Weak ferromagnetism along the triad axis of FeBO3 crystals

Weak ferromagnetic moment along the triad axis of FeBO3 crystals has been calculated on the basis of the single-ion model taking into account the cubic invariant of the crystal field in the spin Hamiltonian.

Flux growth of MBO3 (M=Fe, Ga, In, Sc, Lu) single crystals

The temperatures for saturation of the MBO3 (M=Fe, Ga, In, Sc, Lu) compounds in the M2O3–B2O3– (70 PbO–30 PbF2, wt%) solvents are determined. The growth rates of FeBO3 and GaBO3 crystal faces as functions of the flux supercooling are obtained. It is demonstrated that the bulk FeBO3 and GaBO3 crystals can be grown in a narrow flux supercooling range using a controlled seeding technique. The MBO3 (M=In, Sc, Lu) crystals in the form of (111) plates are synthesized by spontaneous crystallization.

The generalized method of quantitative description of the uniaxial anisotropy in weak ferromagnet rhombohedral calcite type structure crystals with S-state ions

The method for investigation of the uniaxial and hexagonal anisotropies in weakly ferromagnetic rhombohedral FeBO3 crystals with the Fe2+ magnetic impurity with the use of the single-ion and pair approximation has been developed. In the framework of this method, a quantitative discrepancy between theoretical and experimental data on a uniaxial field has been eliminated. The energy contributions to the hexagonal anisotropy that are caused by the Dzyaloshinsky–Moriya interaction, the crystal field of Fe3+ ions and the temperature dependence of this anisotropy were analytically treated. The experimental temperature dependence of the hexagonal anisotropy of FeBO3 crystals is explained. It is shown that the compensation point and the typical temperature dependence of the hexagonal anisotropy result from the competition of the contributions of Fe3+ and Fe2+ ions. It is shown that respective considerable contributions to the anisotropy of Fe3+ and Fe2+ ions are made by the cubic symmetry and the uniaxial symmetry of the exchange “single-ion” type. The anisotropy constants for FeBO3 crystal was obtained by using the described results. It was shown, that for the calcite type structure crystals (iron borate and manganese carbonate) with S-state ions, the single ion and pair models (which previously raised doubts in their validity and accuracy) describe the experimental data good enough.

Electron transport in FeBO3 ferroborate at ultrahigh pressures

The electrical resistance of FeBO3 crystals at high and ultrahigh pressures (up to 198 GPa) and low temperatures has been measured using diamond anvil cells. It has found that in the high-pressure phase, 46 GPa < P < 100 GPa, the activation energy Eac decreases gradually from 0.55 to 0.3 eV according to a linear law. Its extrapolation to zero gives an estimated value of about 210 GPa for the pressure at which complete metallization is expected. However, above 100 GPa, the linear Eac(P) dependence smoothly transforms to a nonlinear one. At the same time, the temperature dependence of the electrical resistance at fixed pressure significantly deviates from the Arrhenius activation law and does not obey the Mott law for the hopping conductivity. Experimental data demonstrate the dependence of the activation energy Eac both on pressure and temperature. At T = 0, the gap tends to zero. Theoretical analysis shows that the decrease in Eac upon cooling can be interpreted in terms of the transition of the low-spin FeBO3 phase to the magnetically ordered (antiferromagnetic) state.

Temperature dependence of the uniaxial magnetic anisotropy of rhombohedral antiferromagnetic crystals with ions in the S state

The contributions of the anisotropic exchange to the firstand second-order uniaxial anisotropy constants have been calculated for hematite at T = 0 K and arbitrary temperatures. The results of the calculations and the most significant mechanisms are taken into account in interpreting the temperature dependence of the anisotropy in rhombohedral antiferromagnetic crystals. The first-order anisotropy constant for hematite is described by the dipole interaction, contributions of the “single-ion” nature, and relatively small contributions of the anisotropic exchange. The second-order constant for hematite includes the “single-ion” contribution and the contribution of the anisotropic exchange. For FeBO3 and MnCO3 crystals, the main contributions to the first-order anisotropy constant come from the dipole and single-ion mechanisms.

Photo-Induced Relaxation Self-Oscillations of Stripe Structures in FeBO&lt;sub&gt;3&lt;/sub&gt;

Photo-induced self-oscillations of stripe structures are studied in FeBO3 crystals at low temperatures. Experimental data show that the observed oscillations have a relaxational character. On the basis of the research carried out, a model for such oscillations is presented.

The energy band structure and optical spectra of FeBO3 calculated with allowance for strong electron correlations

A model of the energy band structure of iron borate (FeBO3) is proposed that combines a one-electron description of the sp states of boron and oxygen with a many-electron description of the d states of iron. The Green functions of d electrons are calculated using the exact Lehmann spectral representation. The energies of the d-type quasiparticles are calculated using terms of the d 4, d 5, and d 6 electron configurations. The optical absorption spectrum of FeBO3 is determined by local excitons and by the electron excitations with charge transfer. The latter excitations control the nature of the dielectric gap in FeBO3 crystals. The model parameters are determined from a comparison to the exciton energies. The density of single-particle states in FeBO3 is calculated. The main bands in the calculated optical absorption spectrum agree well with experimental data for energies up to 3 eV.

Peculiarities in shape of FeBO3 single crystals in the Fe2O3-B2O3-PbO-PbF2 system grown from the flux

The conditions of formation of FeBO3 single crystals in the Fe2O3-B2O3-PbO-PbF2 system are investigated. The solubility of FeBO3 in the solvent 53.3B2O3-32. 7PbO-14.OPbF3 is 7.2 wt% at 854 °C which is the upper maximum temperature of the phase stability of FeBO3. When measuring the growth rates V of FeBO3 single crystal faces for that composition, upon melt supercooling ΔT indicates that V increases linearly along the [111] direction upon ΔT, while the dependence V upon ΔT in the plane (111) exhibits considerable nonlinearity. The growth rate of radial FeBO3 single crystals in the (111) plane is 1.5.10−3 cm/h and in the plane along the [111] direction it is 4.10−4 cm/h on supercooling at 5 °C in dynamic conditions. The nature of the growth rate distribution of FeBO3 single crystal faces upon ΔT suggests that massive specimens may be grown when supercooling at 3–7 °C. FeBO3 crystals are grown by the temperature regime calculated on the basis of experimental data in controlled conditions. The dimensions of FeBO3 crystals are 5×5×1.5 mm3; the linewidth of antiferromagnetic resonance absorption is 30–50 Oe.

Pulse Magnetization Reversal in FeBO3 Crystals

physica status solidi (a)Volume 72, Issue 2 p. K197-K201 Short Note Pulse Magnetization Reversal in FeBO3 Crystals O. S. Kolotov, O. S. Kolotov Moscow State UniversitySearch for more papers by this authorV. A. Pogozhev, V. A. Pogozhev Moscow State UniversitySearch for more papers by this authorR. V. Telesnin, R. V. Telesnin Moscow State UniversitySearch for more papers by this authorG. V. Smirnov, G. V. Smirnov I. V. Kurchatov Institute of Atomic Energy, Moscow Search for more papers by this authorYu. V. Shvydko, Yu. V. Shvydko I. V. Kurchatov Institute of Atomic Energy, Moscow Search for more papers by this authorS. Kadeĉkova, S. Kadeĉkova Physical Institute, Czechoslovak Academy of Sciences, PragueSearch for more papers by this authorM. Kotrbova, M. Kotrbova Physical Institute, Czechoslovak Academy of Sciences, PragueSearch for more papers by this authorJ. Novak, J. Novak Physical Institute, Czechoslovak Academy of Sciences, PragueSearch for more papers by this author O. S. Kolotov, O. S. Kolotov Moscow State UniversitySearch for more papers by this authorV. A. Pogozhev, V. A. Pogozhev Moscow State UniversitySearch for more papers by this authorR. V. Telesnin, R. V. Telesnin Moscow State UniversitySearch for more papers by this authorG. V. Smirnov, G. V. Smirnov I. V. Kurchatov Institute of Atomic Energy, Moscow Search for more papers by this authorYu. V. Shvydko, Yu. V. Shvydko I. V. Kurchatov Institute of Atomic Energy, Moscow Search for more papers by this authorS. Kadeĉkova, S. Kadeĉkova Physical Institute, Czechoslovak Academy of Sciences, PragueSearch for more papers by this authorM. Kotrbova, M. Kotrbova Physical Institute, Czechoslovak Academy of Sciences, PragueSearch for more papers by this authorJ. Novak, J. Novak Physical Institute, Czechoslovak Academy of Sciences, PragueSearch for more papers by this author First published: 16 August 1982 https://doi.org/10.1002/pssa.2210720268Citations: 16 Pl. Kurchatova, 123 182 Moscow, USSR. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Citing Literature Volume72, Issue216 August 1982Pages K197-K201 RelatedInformation