High-temperature heat capacity of YFe3(BO3)4

The molar heat capacity of YFe₃(BO₃)₄ has been measured using differential scanning calorimetry in the temperature range 339–1086 K. It has been found that the dependence C _p = f(T) exhibits an extremum at a temperature of 401 K due to the structural transition.     

Specific heat of YFe3(BO3)4, Y0.5Gd0.5Fe3(BO3)4, and GdFe3(BO3)4

The specific heat was measured in the range 0.4–300 K in YFe₃(BO₃)₄, Y_0.5Gd_0.5Fe₃(BO₃)₄, and GdFe₃(BO₃)₄ single crystals. Sharp anomalies were found at temperatures of first-order structural, second-order antiferromagnetic, and first-order spin-reorientational transitions. A Néel temperature of about 37 K was found to be virtually independent of presence of rare-earth ions, indicating rather weak coupling of Gd and Fe subsystems. The contribution of the magnetic system to specific heat was separated through the scaling procedure allowing determination of the magnetic entropy of Fe and Gd subsystems. At the lowest temperatures, the specific heat in GdFe₃(BO₃)₄ exhibits a Schottky-type anomaly, which is due to Gd³⁺ eightfold degenerate ground-level splitting by the internal magnetic field of the Fe subsystem of about 7 T. The text was submitted by the authors in English.     

Vibrational spectra and elastic,piezoelectric, and magnetoelectric properties of HoFe3(BO3)4 and HoAl3(BO3)4 crystals

Raman spectra of light are obtained for HoFe₃(BO₃)₄ and HoAl₃(BO₃)₄ crystals at various temperatures and are used for determining the frequencies of crystal lattice vibrations at the center of the Brillouin zone. It is also found that the HoFe₃(BO₃)₄ crystal exhibits a phase transition at T _c ≈ 366 K. The magnetoelectric effect in the paramagnetic phase of these compounds is studied experimentally. The lattice vibration frequencies, elastic and piezoelectric moduli, Born dynamic charges, and the high-frequency permittivity are calculated using the density functional method. A peculiar behavior of the transverse acoustic vibration branch is observed in the Γ → Z direction of the Brillouin zone of the HoFe₃(BO₃)₄ crystal. The electric polarization induced by an external field is estimated using the calculated values of piezoelectric moduli and experimental values of magnetostriction.     

IR active phonons in single crystals RFe3(BO3)4 (R = Pr,Nd, and Sm)

We have studied the reflection and transmission spectra of multiferroics RFe₃(BO₃)₄ (R = Pr, Nd, and Sm) at room temperature. Simulation of reflection spectra by the dispersion-analysis method have allowed us to determine the frequencies and oscillator strengths of the majority of IR active A ₂ and E vibrational modes.     

6 MHz BAW resonators fabricated using new piezoelectric crystals PrCa4O(BO3)3 and NdCa4O(BO3)3

Thickness shear mode Bulk Acoustic Wave (BAW) resonators with frequency of 6 MHz, were fabricated using monoclinic piezoelectric crystals PrCa₄O(BO₃)₃ (PrCOB) and NdCa₄O(BO₃)₃ (NdCOB). Zero temperature coefficient of frequency (TCF) characteristics were achieved over the temperature range of –140 °C to 200 °C for (YXt)–1.5° cut PrCOB and (YXt)15° cut NdCOB, with the turnover temperature at 20 °C. The electromechanical coupling factor k₂₆ and the piezoelectric coefficient d₂₆ were determined to be 30.2% and 15.8 pC/N for PrCOB, 29.0% and 15.1 pC/N for NdCOB resonators, respectively. The temperature independent frequency behavior, large coupling factor, high piezoelectric coefficient, together with noticeable mechanical quality factors (Q > 2,500), make PrCOB and NdCOB crystals good candidates for sensing applications with expanded temperature usage range. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Antiferromagnetic resonance in CuB2O4 single crystal

The frequency-field, temperature, and angular dependences of the antiferromagnetic resonance parameters for the tetragonal CuB₂O₄ single crystal are studied in the frequency range 2.6–80 GHz and at temperatures of 4.2–30 K. The results obtained confirm the fact that, in the high-temperature state in the range 10–21 K, this compound is an easy-plane weak ferromagnet. The temperature dependence of the Dzyaloshinski field is determined. An abrupt change observed in the frequency-field dependence of the magnetic resonance at T=4.2 K and H ⊥ C ₄ indicates the transition to the weak ferromagnetic state induced by the external field H _⊥. The phase diagram for CuB₂O₄ is constructed on the H _⊥-T coordinates. It is demonstrated that, in the low-temperature state, the magnetic moments of copper ions remain in the basal plane, but the weak ferromagnetism is absent.     

Features of the magnetic and magnetoelectric properties of HoAl3(BO3)4

The main features of the magnetic and record magnetoelectric properties of a HoAl₃(BO₃)₄ aluminoborate single crystal have been studied experimentally and theoretically. It has been found that the electric polarization that was previously detected in HoAl₃(BO₃)₄ and is record for multiferroics is significantly larger, ΔP _ba (B _a ) ≈ ?5240 μC/m², with an increase in the magnetic field to 9 T at T = 5 K. The measured magnetic properties and revealed features have been interpreted within a united theoretical approach based on the molecular field approximation and on calculations in the crystal field model for a rare-earth ion. The experimental temperature (from 3 to 300 K) and field (up to 9 T) dependences of the magnetization have been described. The parameters of the crystal field of trigonal symmetry for a Ho³⁺ ion in HoAl₃(BO₃)₄ have been determined from the interpretation of the experimental data.     

Spectroscopic properties and structure of the ErFe3(BO3)4 single crystal

Single crystals of the ErFe₃(BO₃)₄ borate were synthesized and their structure was studied. Absorption spectra of the Er³⁺ ion in σ- and π-polarizations of f-f transitions ⁴ I _15/2 → ⁴ I _13/2, ⁴ I _11/2, ⁴ I _9/2, ⁴ F _9/2, ⁴ S _3/2, ² H _11/2, and ⁴ F _7/2 were measured. The refractive index and birefringence were measured as a function of the wavelength. The transition intensities were analyzed within the Judd-Ofelt theory, and the following parameters of the theory were obtained: Ω₂ = 7.056 × 10^?20 cm², Ω₄ = 1.886 × 10^?20 cm², and Ω₆ = 2.238 × 10^?20 cm². Using these parameters, the radiative transition probabilities, luminescence branching ratios, and radiative lifetimes of multiplets were calculated.     

Magnetization and specific heat of DyFe3(BO3)4 single crystal

We present thermodynamic and magnetic studies of single crystalline DyFe₃(BO₃)₄. The data indicate an easy axis antiferromagnetic order below T_N~ 38 K which we attribute to the Fe subsystem. The Dy subsystem remains paramagnetic down to the lowest investigated temperatures of 2 K, but it is polarized by the Fe spins due to a f-d interaction. External magnetic field leads to a spin-flop transition in the iron subsystem as well as to superposed magnetization in the Dy subsystem. The repopulation of two low-lying Kramers doublets in Dy³⁺ ions results in well defined Schottky anomalies in specific heat and magnetization.     

On the deuteron magnetic resonance in single crystals of ND4Cl and ND4Br

The deuteron quadrupole coupling constants in ND₄Cl and ND₄Br have been measured. The results are 179.9±2.0 and 180.0±2.0 kHz, respectively. From the temperature dependence of the line width in ND₄Cl for the d. c. magnetic field along [100] the hindered rotation potential barrier of the ND₄ ⁺-ion was found to be 5.1 kcal/mole. In crystals containing moisture a narrow line component was observed, which is probably due to the formation of an eutectic solution.     

(1)H and (87)Rb nuclear magnetic resonance study of the order-disorder phase transition of RbHSeO(4) single crystals

The ferroelectric phase transition at T(C2) (=370K) in RbHSeO(4) has been studied by (1)H and (87)Rb solid-state NMR. Although not large, the spin-lattice relaxation time, T(1), and the spin-spin relaxation time, T(2), of rubidium and of the alpha- and beta-type protons show distinct change near the phase transition. The intensity of the signal due to the alpha-type protons decreases with increasing temperature, and the intensity of alpha-type protons is quite weak above 330K: at a temperature which is about 40K lower than the phase transition temperature, the ordering of the alpha-type protons occurs. The alpha-type protons in the ferroelectric phase lead to a noticeable change in the proton magnetic resonance spectra. Our study of the (1)H spectra shows that the ferroelectric phase transition in RbHSeO(4) is of order-disorder type and is due to the ordering of protons in hydrogen bonds.     

On the parameters of the magnetocrystalline anisotropy of U3P4 and U3As4 single crystals

Conclusion The change from the zero to the first approximations is accompanied by the change of the sign ofK ₁,K ₂ ¹ being of the same order asK ₁ ¹ . It implies that the neglection of further members of the expansion in (2) may not be quite right. Therefore it might be better to take into consideration also the effect of the further members in (5), but in such a case equation (7) would contain so many unknown parametersK _i ^j , that another way how to solve it would be necessary. In our case, (7) is an equation of a tangent to the curveK ₁ ⁰ =f(1–x ²) at const.H, which has enabled us to determine the dependencesK ₁ ¹ (T, H) andK ₂ ¹ (T, H). Generally, there are other methods of studying the parametersK _i ^j (based on the analysis of torque curves for example) which are more suitable in similar cases, but these methods usually allow necessary measurements only in the fields considerably less than those used in [5].     

Magnetocrystalline anisotropy and magnetostriction of Fe-Si-Al (Sendust) single crystals

The magnetocrystalline anisotropy constant, K₁ and the magnetostriction constants, λ₁₀₀ and λ₁₁₁ for the Sendust alloys were determined at 300 K in the composition region, 7.5–11.0 wt%Si, 4.0–7.0 wt%Al, bal. Fe. The line of K₁ = 0 in the Fe-Si-Al alloy system was found to lie around 7.0–9.5 wt%Si, 5.5 wt%Al, bal.Fe and 9.5 wt%Si, 5.5–7.0 wt%Al bal.Fe compositions. The line of λ_s = 0 was also determined as a function of Fe, Si and Al contents. Both lines of K₁ = 0 and λ_s = 0 intersect at the composition, 9.6 wt%Si, 5.5 wt%Al, bal.Fe. This alloy composition is close to those for alloys with high initial and maximum permeabilities. The line of K₁ = 0 determined by the present experiment is found to be different from that of Zaimovsky and Selissky. The line of λ_s = 0 is similar to their results.     

Spectroscopy of phonon and vibronic states of YbAl3(BO3)4 single crystal

The polarized Raman and reflection spectra of a single crystal YbAl₃(BO₃)₄ at room temperature were studied. Raman active vibrational modes A ₁, E _TO, and E _LO are identified. In the Raman spectrum, we detected an intense line at a frequency of 1018 cm⁻¹, which refers to internal vibrations of the BO₃ group and is known to be promising for use in amplifiers based on stimulated Raman scattering. From the simulation of reflection spectra by the method of dispersion analysis the frequencies of A ₂ vibrational modes were determined. Intense bands observed in the low-temperature transmission spectra in the range of f-f transitions in the Yb³⁺ ion are attributed to electron-phonon transitions. The Raman lines are compared with electron-phonon lines in the transmission spectrum.     

Magnetic anisotropy of the SrCu2(BO3)2 system as revealed by X-band ESR

X-band electron paramagnetic resonance measurements on a single crystal of the highly frustrated SrCu₂(BO₃)₂ system are shown to provide an essential inspection of the magnetic anisotropy present in this compound. The very broad absorption lines seem to be consistent with the largest anisotropy term, namely, the antisymmetric Dzyaloshinsky-Moriya (DM) interaction allowed by symmetry. However, the previously well-accepted model of only interdimer interaction is generalized with additional intradimer DM terms. Moreover, spin-phonon coupling is recognized as the cause of the line width broadening with increasing temperature.     

Intracavity second-harmonic generation of 1.06 μm in GdCa4O(BO3)3 crystals

The characteristics of intracavity second-harmonic generation (SHG) at 1.06 μm in GdCa₄O(BO₃)₃ (GdCOB) crystals cut for different type I phase-matching (PM) directions of (θ,φ)=(66.8°, 132.3°); (19.4°, 0°); (90°, 46°) have been investigated. It was found that the intracavity SHG was significantly efficient in the PM direction of (66.8°, 132.3°), and that the intrinsic lower effective nonlinear coefficient (d_eff) was responsible for the less-efficient SHG in the other two directions. A maximum CW SHG output power of 2.81 W was obtained with an optical conversion efficiency of 18.7%, while the corresponding effective intracavity SHG efficiency was determined to be 41.3%. The intracavity SHG efficiency of GdCOB has been found to reach two-thirds of that obtained with type II phase-matching KTiOPO₄ (KTP). Received: 26 April 2000 / Revised version: 3 July 2000 / Published online: 5 October 2000     

Determination of the magnetic structure of SmFe(3)(BO(3))(4) by neutron diffraction: comparison with other RFe(3)(BO(3))(4) iron borates

Temperature dependent neutron diffraction studies were performed on SmFe(3)(BO(3))(4). The crystallographic structure was determined to stay as R32 over the whole studied temperature range of 2?K?相似文献   

Comparison of the Absorption Spectra of Nd3+ Ions in the NdFe3(BO3)4, Nd0.5Gd0.5Fe3(BO3)4, and Ho0.75Nd0.25Fe3(BO3)4 Crystals

Physics of the Solid State - The polarized optical absorption spectra in the region of a series of the f–f  transitions of Nd3+ ions in the Ho0.75Nd0.25Fe3(BO3)4,...