FeBO3 Crystal Research Articles

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.

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.

Magnetic-field-induced orientational phase transition in a nonuniformly stressed iron borate single crystal

Spatially nonuniform magnetic anisotropy was induced in the basal plane of an iron borate (FeBO3) single crystal by applying low-symmetry stresses. The effect of nonuniform magnetic anisotropy on the magnetic state of this weak ferromagnet was studied by magnetooptic methods. It is revealed that, when a nonuniformly stressed FeBO3 crystal is magnetized in the basal plane along a certain direction (depending on the symmetry of the applied stress), a transition from a uniform to a spatially modulated magnetic state occurs, which is not observed in the crystal in the absence of stresses. The modulated magnetic phase of the crystal can be represented as a static spin wave linearly polarized in the basal plane, with the azimuth of the weak-ferromagnetism vector oscillating about the direction of the mean magnetization. The temperature and field dependences of the spatial period of the modulated magnetic structure and the amplitude of oscillations of the ferromagnetism vector are studied, and the temperature dependence of the field range over which the modulated phase exists in the nonuniformly stressed FeBO3 crystal is found. The results are discussed in terms of the phenomenological theory of magnetic phase transformations. It is shown that the theoretical model used consistently describes all the experimental results of the study of the noncollinear magnetic phase of the nonuniformly stressed FeBO3 crystal.

Technical magnetization of the nonuniformly stressed iron borate single crystal

Additional spatial nonuniform magnetic anisotropy is induced in the basal plane of a FeBO3 single crystal using low-symmetry mechanical stresses. The effect of the nonuniform magnetic anisotropy on the magnetic state of this weak easy-plane ferromagnet is studied by a magnetooptic method. When the nonuniformly stressed FeBO3 crystal is magnetized in the basal plane near a certain preferential direction, the crystal is found to transform from a homogeneous into a spatially modulated magnetic state, which can be represented by a static spin wave in which a local ferromagnetism vector lies in the basal plane and oscillates about the average magnetization direction in the crystal.

Modulated magnetic structure of a nonuniformly stressed FeBO3 single crystal

The magnetization of a nonuniformly stressed FeBO3 crystal along any of the two specific directions in the basal plane (the easy plane) at a temperature of T < 140 K in a magnetic field exceeding the threshold value H0 is found to lead to a transition of the crystal from the uniform magnetic state to the spatially modulated one. The modulated magnetic phase arising under these conditions exists in a certain temperature-dependent field range H0 ≤ H ≤ Hc and is representable in the form of a static spin wave that is linearly polarized in the easy plane of the crystal and has a wave vector k oriented at an angle of ∼30° to the magnetization axis. The field, temperature, and orientation dependences of k are investigated. A physical mechanism is proposed to explain the modulation of the magnetic order parameter of the crystal under study. The results obtained are discussed in terms of the magnetic ripple theory.

Structural and electronic transitions in gadolinium iron borate GdFe3(BO3)4 at high pressures

The optical properties and structure of gadolinium iron borate GdFe3(BO3)4 crystals are studied at high pressures produced in diamond-anvil cells. X-ray diffraction data obtained at a pressure of 25.6 GPa reveal a firstorder phase transition retaining the trigonal symmetry and increasing the unit cell volume by 8%. The equation of state is obtained and the compressibility of the crystal is estimated before and after the phase transition. The optical spectra reveal two electronic transitions at pressures ∼26 GPa and ∼43 GPa. Upon the first transition, the optical gap decreases jumpwise from 3.1 to ∼2.25 eV. Upon the second transition at P=43 GPa, the optical gap deceases down to ∼0.7 eV, demonstrating a dielectric-semiconductor transition. By using the theoretical model developed for a FeBO3 crystal and taking into account some structural analogs of these materials, the anomalies of the high-pressure optical spectra are explained.

Double-crystal diffraction imaging with a small effective divergence source: application to the magneto-acoustic vibrations in FeBO3

Ultrasonic standing waves, excited in FeBO3(111) crystal plates through magneto-elastic coupling, were visualized using monochromatic Bragg diffraction imaging (topography) with synchrotron radiation. The images depend strongly on whether diffraction by the sample occurs in the same plane as in the double-crystal monochromator, or in the perpendicular plane. The observations are explained by taking into account (a) the strong spatial dispersion which prevails because of the small effective divergence (angular size of the source as seen from a point in the specimen), which is less than one microradian in this experiment, and (b) the sample vibration and curvature.

Section and stroboscopic diffraction imaging of themagneto-acoustic vibrations in FeBO3by synchrotron radiation

Ultrasonic waves, excited in an FeBO3 crystal via magneto-elastic coupling, were visualized using synchrotron radiation diffraction imaging (`topography'). In particular, restricted volume images were used in order to distinguish the contribution of the various parts of a thin (50 µm) sample to the diffracted beam. The magnetic field dependence of the sound velocity was then exploited to tune the FeBO3 crystal at a resonance four times the ESRF single bunch frequency, allowing stroboscopic section imaging and the deconvolution of the time-integration effect. This set of experiments confirmed that the vibrating crystal model used to explain the focusing of x-rays in FeBO3 at certain resonances is correct.

Synchrotron Radiation Diffraction Imaging Study of the Magnetoacoustically Induced X-Ray Focusing Effect in FeBO3

ABSTRACTSynchrotron radiation diffraction imaging (‘topography’) was used at the ESRF to visualize ultrasonic standing waves in a magnetoacoustically excited FeBO3 crystal. Images were recorded at long sample-to-film distances (up to 1.5 m) without substantial loss of resolution. The resonant patterns reveal that the crystal acts as a pulsed X-ray focusing lens and strongly depend on both the amplitude of the magnetic field and the sample-to-detector distance. Different resonant frequencies can also lead to more complicated images due to interference effects of several vibrating modes present in the crystal. A model is proposed followed by a numerical integration which predicts the focusing of the X-ray beam and demonstrates the agreement between theory and experiment. This effect could be used to simultaneously monochromatize and focus the X-ray beam.

Studies of nuclear resonant scattering at TRISTAN-AR

Studies of nuclear resonant scattering of synchrotron radiation undertaken with the X-ray undulator installed in the TRISTAN Accumulation Ring at the National Laboratory for High Energy Physics, KEK, are reported. These studies have evaluated the effect of fast magnetic switching on the nuclear collective decay in an FeBO3 crystal, the change in the polarization state of nuclear Bragg scattering by fast magnetic switching, and the influence of this switching on the time evolution of the nuclear forward scattering. The phenomenon of interferometric nuclear forward scattering has also been studied.