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NdFe3(BO3)4 and NdGa3(BO3)4 crystals are of great interest due to their physical properties. For example, NdFe3(BO3)4 crystal demonstrates magnetodielectric and magnetopiezoelectric effects, and NdGa3(BO3)4 crystal possesses luminescent and nonlinear optical properties. In this work, the properties of these materials are calculated by the plane-wave pseudo-potential method based on density functional theory. The structures of the crystals are optimized. The electronic structure of NdFe3(BO3)4 and NdGa3(BO3)4 are calculated. [ABSTRACT FROM AUTHOR]

The direct (MEH-) and inverse (MEE-) magnetoelectric effects in the HoAl3(BO3)4 single crystal are studied. Temperature and magnetic field dependences of permittivity of the crystal are investigated. A relation between the investigated effects was established. It was found that the magnetoelectric effect can exist in crystals without magnetic order or spontaneous polarization. It was shown that the phenomena investigated are due to magnetostriction or magnetoelastic effect. The thermodynamic potential was considered for describing magnetoelectric effect at low magnetic fields. The results obtained are explained within a proposed qualitative microscopic model, based on interplay of configuration of 4f- electron subshell of the rare-earth element and applied magnetic or electric. [ABSTRACT FROM AUTHOR]

Single crystals of SmAl3(BO3)4 were synthesized by the group growth on seeds method. The crystal structure was solved using a single‐crystal experiment and the purity of the bulk material was proved by the Rietveld method. This borate crystallizes in the monoclinic C2/c space group with unit‐cell parameters a = 7.2386 (3), b = 9.3412 (5), c = 11.1013 (4) Å and β = 103.2240 (10)°. IR and Raman spectroscopic analyses confirmed the monoclinic structure of SmAl3(BO3)4. Under 532.1 nm excitation, luminescence spectra exhibit bands assignable to the transitions from 4G5/2 to 6H5/2, 6H7/2, 6H9/2 and 6H11/2. The similarity of the luminescence spectra of the trigonal and monoclinic polymorphs is explained by the minor role of Sm—O bond distortion and the primary role of rotational distortion of SmO6 octahedra. The smaller covalency of the Sm—O bond in alumoborates is deduced in comparison with galloborates. Calorimetric measurements did not reveal high‐temperature structural phase transitions up to a temperature of 720 K. [ABSTRACT FROM AUTHOR]

The Raman spectra of the TbFe2.5Ga0.5(BO3)4 single crystal in the temperature range from 8 to 400 K have been observed. The condensation and restoration of the soft modes have been found. The soft modes are associated with the structural phase transition from the R32 phase to the P3121 phase. The behavior of the hard modes confirms the structural phase transition close to the tricritical point. The temperature of the structural phase transition T1 = 33 K is established. [ABSTRACT FROM AUTHOR]

Single crystal of HoGa3(BO3)4 has been grown using solution-melt synthesis. The optical band gap determined from the measured absorption spectrum is due to direct allowed transition and equals to 4.14 eV. The optical properties of this crystal are calculated by the plane-wave pseudo-potential method based on density functional theory. The structure of the crystal has been optimized. The electronic structure of HoGa3(BO3)4 is calculated. The experimental and theoretical fundamental absorption spectra are compared. The calculated bandgap is in good agreement with the experimental data. [ABSTRACT FROM AUTHOR]

Europium gallium garnet (EuGG) single crystals were grown from fluxes with various contents. Optical absorption spectra of EuGG grown from a flux containing calcium show an additional band in the ultraviolet and blue regions of the spectra as compared to the case of a calcium-free flux. Mössbauer spectra of the samples grown from the fluxes with different additives show no signs of other valence states of the europium ions except for 3+. However, they indicate changes in the crystal field due to the entrance of additive ions. The nature of the additional absorption must be the same as that for calcium-doped gadolinium gallium garnet, i.e., anion vacancies. Mössbauer isotope shifts and quadrupole splitting for EuGG are determined. [ABSTRACT FROM AUTHOR]

A substantial magnetic contribution into specific heat capacity is found in monocrystalline ErAl3(BO3)4 at temperatures below 5 K. The results of measured ESR spectra at 4,2 K confirm manifestation of short-range magnetic order as well. The obtained data is discussed invoking the model accounting for spin-spin interaction between rare-earth ions in paired clusters. [ABSTRACT FROM AUTHOR]

The optical absorption spectra of an easy-plane NdFe3(BO3)4 antiferromagnet are measured in the region of the 4I9/2 → 2H11/2 transition of the of Nd3+ ion. The study is performed in the 2–35 К temperature range, in external magnetic fields of up to 65 kOe directed both along the С3 axis and the basal plane of the crystal. The splitting values of the Nd3+ excited states in the exchange field of the Fe3+ subsystem and the g-factors of the 2H11/2 multiplet states are determined. The nontrivial dependences of the splitting of some Nd3+ states in a magnetic field indicate that these states have anisotropic Fe–Nd exchange interaction. [ABSTRACT FROM AUTHOR]

The main components of the tensor of the moduli of elasticity and the piezomodulus have been measured in monocrystals of the ferroborate HoFe3(BO3)4. The spin-dependent contributions to sound velocity, dielectric permeability, and piezoelectric response in the antiferromagnetic state were studied. The parameters of magnetoelectric and magnetoelastic interactions in an easy-plane magnetic-ordering phase have been defined. A phenomenological interpretation of observed effects is given. [ABSTRACT FROM AUTHOR]

Experimental AFMR studies of crystalline PrFe3(BO3)4 over a wide frequency range of 10–143 GHz at a temperature of 4.2 K have been carried out. The high-frequency properties of praseodymium ferroborate are well described in terms of a model of a two-sublattice antiferromagnet with an “easy axis” anisotropy. An energy gap of 134.3 ± 0.5 GHz is determined and the magnitude of the effective magnetic anisotropy field is estimated to be 1.9 ± 0.1 kOe. An analysis indicates that the spin-orientational phase transition in this compound is a first order transition. [ABSTRACT FROM AUTHOR]

Raman spectra of a HoFe3(BO3)4 crystal chip has been investigated at simultaneously high temperature and high pressure (up to 7.1 GPa and 560 K). On the basis of Raman analysis, the assignment to one of the two possible crystal phases has been made. The experimental p- T phase diagram of HoFe3(BO3)4 was established. An increase in the pressure leads to an increase in the temperature of transition. The phase boundary equation was obtained. Neither triple points nor a phase with new symmetry was revealed in the phase diagram. A critical point with the temperature T = 560 K and the pressure p = 2.53 GPa was found. The nanocrystals with different shapes began to grow on crystal surface after reaching that point. The composition of new nanocrystals is identical to the composition of initial crystal. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]