Contemporary Apparatus for Single Crystals Growth of Oxide Compounds and Metals by Optical Floating Zone (FZ)

A contemporary apparatus with radiation (light) heating for growth of single crystals of refractory oxides and metals is described. To reduce the dissociation or evaporation of the melt or crystal components, the growth process was carried out in oxygen or an alternative gas at pressures up to 100 bar. The annealing system applied directly in the growth process at 1650 °C under O2 pressure and at temperatures up to 2500 °C under protective gas flow, allows the obtaining of large and perfect single crystals. Many single crystals of oxide materials, including incongruently melting substances, such as Y3Fe5O12, Gd3Fe5O12, BaFe12O19, SrFe12O19, BaFe12-x AlxO19, and many others have been grown, and much more could be grown

Growth and X‑ray Diffraction Study and Specific Features of Thermal Expansion of Ba₃NbFe₃Si₂O₁₄ Single Crystal from the Langasite Family

Ba₃NbFe₃Si₂O₁₄ single crystals of promising multiferroic properties from the langasite family have been grown by floating zone melting. The accurate high-resolution X-ray diffraction studies of this crystal were performed on a diffractometer with a two-dimensional CCD detector at 293 and 90.5 K. To compensate systematic measurement errors, two data sets were obtained independently for different sample orientations at each temperature. The structure refinement was performed based on averaged data sets with the following results: space group <i>P</i>321, <i>Z</i> = 1; <i>a</i> = 8.52421(8), <i>c</i> = 5.23372(5) Å at 293 K; and <i>a</i> = 8.5211(2), <i>c</i> = 5.2243(7) Å, at 90.5 K. The <i>R</i> factors of the model structure refinement were found to be <i>R</i>/<i>wR</i> = 1.15/1.29% for 4396 independent reflections at 293 K, and <i>R</i>/<i>wR</i> = 1.13/1.35% for 4203 reflections at 90.5 K. A displacement of magnetic ion Fe³⁺ in the 3<i>f</i> site was found with reducing temperature. It was also established from comparison of the structures of Ba₃NbFe₃Si₂O₁₄ and Ba₃TaFe₃Si₂O₁₄ that the mobility of the cation in the 3<i>f</i> sites changes with an isomorphic substitution of Nb cations by Ta in the octahedral sites. This can change the characteristics of the structure and magnetic helix responsible for multiferroic properties of the iron-containing langasites. An anomaly in thermal expansion is found in the Ba₃NbFe₃Si₂O₁₄ crystal. When the temperature is reduced, the compression ratio along the <i>c</i> axis is about two times larger than that along the <i>a</i> axis, which is not typical of other langasite-family crystals

Laser-induced magnetization precession in the magnetite Fe₃O₄ in the vicinity of a spin-reorientation transition

Using time-resolved magneto-optical pump-probe technique we demonstrate excitation of magnetization precession in a single crystalline bulk magnetite Fe3O4 below and in the vicinity of the Verwey and spin-reorientation (SR) phase transitions. Pronounced temperature dependence of the precession amplitude is observed suggesting that the excitation occurs via laser-driven spin-reorientation transition. Similarity observed between the characteristic features of the laser-induced ultrafast SR and Verwey transitions suggests that they both rely on the same microscopic processes.publishe