Optical Floating Zone Furnace Research Articles

Growth and characterization of perovskite TbMnO3 single crystal: Structural, vibrational and magnetic properties

In this study, we have successfully grown a high-quality single crystal of perovskite TbMnO3 utilizing an optical floating zone furnace under an air atmosphere. To ensure the crystal purity and orientation, we probed X-ray diffractometer (XRD) and X-ray Laue photographic analysis, respectively. The XRD analysis confirmed that TbMnO3 ceramics possess a distorted orthorhombic perovskite structure (Pbnm). By analyzing the X-ray absorption and vibrational modes via Raman spectroscopy, we not only confirmed the pure phase of the TbMnO3 sample but also gained valuable insights. In terms of magnetic properties, we conducted measurements in two different orientations: H||a and H||c. Notably, there were no successive transitions observed along the H||a direction, but along H||c, we observed three successive transitions with decreasing temperature at TN = 41 K, TS = 28 K, and TNTb = 7 K. Below TN (41 K), there is an unusual softening observed in one of the first order phonon modes, indicating a robust connection between spin and phonon interactions. The magnetic phase transition along both axes validates the presence of magnetic anisotropy in the prepared single crystal, as indicated by magnetic susceptibility. The negative θcw value along the a-axis and the positive θcw value along the c-axis suggest a competition between antiferromagnetic and ferromagnetic interactions in the ac-plane.

Magnetic-field-induced spin reorientation in TmFeO<sub>3</sub> single crystals

TmFeO<sub>3</sub> exhibits rich physical properties such as magneto-optical effect, multiferroicity, and spin reorientation, making it possess significant research value in condensed matter physics and materials science. In this study, we utilize a time-domain terahertz magneto-optical spectroscopy system to investigate the changes in spin resonance frequency of TmFeO<sub>3</sub> single crystal at <i>T</i> = 1.6 K under external magnetic fields in a range of 0–7 T. The TmFeO<sub>3</sub> sample is grown in an optical floating zone furnace and its crystallographic orientation is determined by using back-reflection Laue X-ray photography with a tungsten target. The measurement setup is a self-built time-domain terahertz magneto-optical spectroscopy system, with magnetic fields in a range of 0–7 T, temperatures in a range of 1.6–300 K, and a spectral range of 0.2–2.0 THz. A pair of 1 mm-thick ZnTe nonlinear crystals is used to generate and detect terahertz signals through optical rectification and electro-optic sampling technique. The system variable temperature and magnetic field are controlled by a superconducting magnet. In experiments, a linearly polarized terahertz wave is vertically incident on the sample surface, and its magnetic component <i>H</i><sub>THz</sub> is parallel to the sample surface. By rotating the sample, the angle (<i>θ</i>) between macroscopic magnetic moment <i> <b>M</b> </i> and <i>H</i><sub>THz</sub> can be tuned, achieving selective excitations of the two modes, that is, <i>θ</i> = 0 for q-AFM mode and 90° for q-FM mode. Terahertz absorption spectrum results indicate that as the magnetic field increases, the quasi-ferromagnetic resonance (q-FM) of TmFeO<sub>3</sub> single crystal shifts towards high frequencies, and quasi-antiferromagnetic resonance (q-AFM) transits to q-FM under low critical magnetic fields (2.2–3.6 T). Through magnetic structure analysis and theoretical fitting, it is confirmed that the magnetic moment of the single crystal undergoes magnetic field induced spin reorientation. This study is helpful in better understanding of the regulation mechanism of the internal magnetic structure of rare earth ferrite under the combined action of external magnetic field and temperature field, and also in developing related spin electronic devices.

Optical and scintillation properties of the Eu2O3-doped HfO2-Al2O3–SiO2 glass ceramics

In this study, Eu-doped 10HfO2–10Al2O3–80SiO2 glass ceramics with different Eu concentrations were prepared by the melt-quenching method using an optical floating zone furnace, and optical and scintillation properties were investigated to apply them for radiation detectors. All the glass ceramic samples were transparent, although they included not only an amorphous phase but also a crystal phase of cubic-HfO2. Photoluminescence and scintillation peaks due to Eu2+ were detected at 400–550 nm. In the glass ceramic samples with higher Eu concentration, the luminescence of Eu3+ was also observed. Quantum yields and afterglow levels decreased with increasing Eu concentration. The 1.0% Eu-doped sample had the highest light yield among all our glass samples, and the light yield was 630 photons/MeV under γ-ray irradiation from 137Cs.

Tunable magnetic phase transition in thulium–samarium orthoferrite single crystals

Spintronics and condensed matter physics are in pursuit of materials that can serve as carriers for novel quantum devices. Antiferromagnetic rare earth orthoferrites (RFeO3, where R is rare earth or Y), are potential functional materials for magnetic information processing. They exhibit temperature-controlled spin reorientation transition (SRT) and magnetic field/temperature-induced spin switching (SSW) properties. As such, RFeO3 is expected to be used in spintronic devices that can easily control the spin. With the advancement of research, the co-doping of rare earth ions has emerged as a prominent area of investigation in RFeO3. In this work, we have grown a series of Tm1-xSmxFeO3 (TSFO, x = 0, 0.2, 0.3, 0.4) single crystals via a four-mirror optical floating zone furnace. Crystal axes and single phase of these single crystals were determined using Laue back reflection camera and X-ray diffractometer. We observed that the doping of Sm ions can effectively regulate the spin reorientation temperature of the parent material TmFeO3. Both type-I and type-II SSW have been observed when the doping rate x is 0.2 or 0.4, perfectly integrating the magnetic properties of TmFeO3 and SmFeO3 single crystals. Furthermore, the spin switching in TSFO (x = 0.2, 0.3, 0.4) can be manipulated by applying low magnetic fields with tens of Oe. On the other hand, when the doping rate x reaches 0.4, the magnetic compensation phenomenon and the Néer temperature of rare earth ions occurred. The super-exchange interaction between R3+ and Fe3+ magnetic sublattices leads to these interesting phenomena.

The surface tension of Ga2O3 melt measured by a drop-weight method in an optical floating-zone furnace

The surface tension of Ga2O3 melt is successfully measured using a drop-weight method in an optical floating-zone furnace that we have developed. The method is verified to be feasible by measuring the surface tension value of TiO2 melt and then comparing it with values in previous reports determined by other methods. We find that the surface tension of Si-doped Ga2O3 melt increases with the decrease in the Si doping concentration and reaches 527.9 mN m−1 for pure Ga2O3 melt. The surface tension of the unintentionally doped Ga2O3 melt is also measured to be 519.3 mN m−1 in the presence of some common contaminants appearing in Czochralski and edge-defined film-fed growth methods, including Ir, Al, and Si.

Low field spin switching of single crystal TmFeO3

High quality TmFeO3 single crystal with the length of 50 mm has been prepared by using a four-mirror optical floating zone furnace. X-ray diffractometer and Laue back reflection camera are used to determine the quality and crystal orientations of TmFeO3 single crystal. Here, the magnetic properties of TmFeO3 single crystal in low magnetic fields are studied systematically. A typical spin reorientation transition from Γ4(Gx, Ay, Fz) configuration to Γ2(Fx, Cy, Gz) configuration is observed in TmFeO3 single crystal with the temperature between 82 K and 95 K. Temperature-induced type-II spin switching in both a-axis and c-axis are observed in field cooling and measuring while cooling (FCC) and field cooled and measuring while warming (FCW) modes, which has not been reported in previous researches on TmFeO3 single crystal. This is an extremely rare occurrence within the RFeO3 family. The results suggest that such spin switching is easily susceptible to very low external magnetic fields. Therefore, by adjusting the magnitude of the external magnetic fields, the triggering temperatures of spin switching can be controlled, which offers the possibility of the application for TmFeO3 single crystal in future spintronic devices.

Ordered and disordered variants of the triangular lattice antiferromagnet Ca3NiNb2O9 : Crystal growth and magnetic properties

Single crystals of the triangular lattice antiferromagnet (TLAF) ${\mathrm{Ca}}_{3}{\mathrm{NiNb}}_{2}{\mathrm{O}}_{9}$ and its nonmagnetic analog ${\mathrm{Ca}}_{3}{\mathrm{MgNb}}_{2}{\mathrm{O}}_{9}$ are grown using the four-mirror optical floating-zone furnace. By varying the growth conditions, two types of mm-sized crystals are obtained: monoclinic crystals of the form ${\mathrm{Ca}}_{3}{\mathrm{NiNb}}_{2}{\mathrm{O}}_{9}$ where ${\mathrm{Ni}}^{2+}$ and ${\mathrm{Nb}}^{5+}$ exhibits 1:2 ordering and Ni ions (spin 1) are arranged on a triangular lattice, and orthorhombic crystals of the form ${\mathrm{CaBO}}_{3}$ where B site is occupied randomly by 1/3 Ni and 2/3 Nb. Low-temperature specific heat and low-field magnetization on these crystal modifications revealed contrasting ground states. In B-site ordered ${\mathrm{Ca}}_{3}{\mathrm{NiNb}}_{2}{\mathrm{O}}_{9}$, the Ni spins undergo two successive phase transitions at ${\mathrm{T}}_{{\mathrm{N}}_{1}}=4.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${\mathrm{T}}_{{\mathrm{N}}_{2}}=4.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The magnetic propagation vector below ${\mathrm{T}}_{{\mathrm{N}}_{2}}$ is found to be $\stackrel{P\vec}{k}=(0,1/3,0)$ confirming the ${120}^{\ensuremath{\circ}}$ spin structure. The high-field magnetization reveals the presence of plateaus characteristic of TLAFs. In contrast, the orthorhombic ${\mathrm{CaBO}}_{3}$ crystals exhibit a spin-glass-like ground state.

Microstructures and mechanical properties of V–V3Si eutectic composites

Abstract V–V3Si eutectic alloys were directionally solidified in a high temperature optical floating zone furnace. Depending on the solidification conditions, several microstructures were observed, such as well-aligned broken lamellar, fibrous, or cellular microstructures. The interphase spacings increased with decreasing solidification rates in agreement with the Jackson-Hunt theory. The mechanical properties of the individual phases were investigated by nanoindentation. It was found that the modulus and nanoindentation hardness of V3Si are 214 and 13.8 GPa, respectively, and those of the V solid-solution are 165 and 3.4 GPa, respectively. The high-temperature strength was examined by tensile testing at elevated temperatures. Preliminary results show that the ductile-to-brittle transition temperature is about 800 °C for this composite, and its strength is significantly higher than conventional V solid-solution alloys.

Compositional screening of Ce-doped (Gd,Lu,Y)3(Al,Ga)5O12 ceramics prepared by quenching from melt and their luminescence properties

Quenching from the melt using an Optical Floating Zone furnace was investigated as a possible high-throughput preparation method in order to screen novel scintillating materials. To validate this method, polycrystalline rare-earth aluminum garnets and yttrium gallium aluminum garnets were synthesized and characterized by X-ray diffraction, photoluminescence and radioluminescence emission spectra as well as radioluminescence imaging and compared to the previously reported properties of those materials. In order to achieve rapid, but quantitative comparison of the materials, pellets fabricated from the synthesized powders were sintered; two different sintering conditions were investigated and compared. A simplistic energy deposition and light absorption model for brightness of opaque samples under X-ray irradiation was developed to estimate the relative scintillation efficiency of the materials. Based on the results, Y3Al5O12, LuY2Al5O12 and GdY2Al5O12 seem to have the highest scintillation efficiency among the prepared samples.

Directionally solidified Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic high-entropy oxide ceramics with well-oriented structure, high hardness, and low thermal conductivity

Directionally solidified Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic high-entropy oxide ceramics (HEOCs) were successfully prepared with an optical floating zone furnace. The Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic HEOCs were pure phases with uniform distribution of rare-earth elements. The preferred growth orientation relationships were <10−10 > {0001}Al2O3 // <110 > {211}(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12. The indentation fracture toughness and Vickers hardness were 6.8 ± 0.9 MPa·m1/2 and 16.1 ± 0.3 GPa, which were higher than that of Al2O3/Y3Al5O12 eutectic ceramics. The room temperature bending strength was 333 ± 42 MPa. Crack bridging, deflection and bifurcation were the main toughening mechanism. Hardness and reduced modulus mapping results illustrated that the hardness of (Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 was close to that of Al2O3. Thermal expansion coefficient of Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic HEOCs was very similar to that of Al2O3/Y3Al5O12 but thermal conductivity was as low as 4.9 Wm−1 K−1 due to strong lattice distortion. These results suggest that high-entropy Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic ceramics are promising candidates for structural components application in gas turbine engines.

4f-3d interaction dominated field tailoring spin switching in rare earth doped Dy0.5Er0.5FeO3 single crystal

A large single crystal Dy0.5Er0.5FeO3 of 5.2 mm in diameter and 55 mm in length is prepared using the optical floating zone furnace system. The good quality of the single crystal without impurities is confirmed by powder and Laue X-ray diffraction experiments. Magnetic measurements are conducted using 1~2 millimeter cubic sample of Dy0.5Er0.5FeO3 single crystal, which experiences spin switching in two measurement modes of zero-field-cooling (ZFC) and field-cooling (FC) magnetization vs temperature (M-T) curves under magnetic fields less than 48 Oe. The co-occurrence of spin switching (i.e. magnetization drop in FC mode and magnetization jump in ZFC mode) has not been reported in the parent materials of DyFeO3 and ErFeO3 single crystals. More interestingly this kind of spin switching can be easily tailored by using low fields in a large temperature range from below 50 K to nearly 400 K. Spin reorientation transition occurs near 35.9-48 K, where the spin configuration of the iron sublattice changes from Γ4 and Γ2. The magnetic interaction between (Dy, Er)-4f and Fe-3d electrons in the two different sublattices of Dy0.5Er0.5FeO3 single crystal which governs the spin reorientation transition and spin switching under different temperature and magnetic field are discussed.

Automated extraction of physical parameters from experimentally obtained thermal profiles using a machine learning approach

Computational modeling is playing an increasingly important role in designing novel experiments and enhancing existing ones. However, these models require input parameters that are sufficiently accurate in order for the predictions to be quantitatively reliable. Frequently, some of these parameters are not directly measurable or have a large uncertainty. We propose a machine learning approach to automatically extract these uncertain or unknown parameters indirectly from experimental measurements that depend on the combination of parameters in a complex manner. The algorithm iteratively refines the possible range of each parameter based on the mean and standard deviation of the sampling simulations that are at the 10th percentile or lower in error until the convergence criteria is met, which is followed by a multivariate quadratic fit and minimization. To demonstrate its applicability, we apply the algorithm to determine physical parameters during the fitting of temperature profiles extracted from in situ synchrotron measurements of an optical floating zone furnace used for high-temperature crystal growth. We built a thermal transfer model in COMSOL Multiphysics® software that considers an Al2O3 sample that is heated by a power source and thermal conduction and cooled due to natural air convection and thermal radiation. A set of experimentally measured steady-state temperature profiles of a heated Al2O3 sample is used as training data to determine the parameter set using the algorithm, which resulted in a close match. Using this parameter set, we also simulated the time-dependent temperatures, which yielded good agreement to the corresponding experimental measurement. We conclude that the steady-state temperature profiles suffice as training data, eliminating the need for additional in situ measurements of the dynamic experimental state for robust model parameterization.

In situ temperature profile measurements with high-energy X-rays as a probe of optical floating zone crystal growth environment

The ability of optical floating zone (OFZ) furnaces to rapidly produce large single crystals of complex emerging materials has had a transformative effect on many scientific fields that require samples of this type. However, the crystal growth process within the OFZ furnace is not well understood owing to the challenges involved in monitoring the high-temperature crystal growth process. Novel beamline-compatible optical furnaces that approximate the inhomogeneous growth environment within an OFZ furnace have been fabricated and tested in high-energy synchrotron beamlines. It is demonstrated that temperature profiles can be effectively extracted from powder diffraction data collected on polycrystalline ceramic rods heated at their tip. Furthermore, these measured temperature profiles can be accurately reproduced using a heat-transfer model that accounts for solid-state thermal conduction, partial sample lamp power absorption, convective air cooling and radiative cooling, allowing key thermal parameters such as thermal conductivity to be extracted from experimental data.

Preferential growth of directionally solidified Al2O3/SmAlO3 eutectic ceramics

Directionally solidified Al2O3/SmAlO3 (SAP) eutectic ceramics were successfully prepared with an optical floating zone furnace. The crystallographic orientation and interfacial structures were investigated by electron backscattered diffraction and transmission electron microscopy. It was found that Al2O3 has one preferred growth direction but the SAP has two. The preferred growth direction of the directionally solidified Al2O3/SAP eutectic ceramics was 〈101¯0〉Al2O3 || 〈100〉SAP || 〈011〉 SAP. The near-coincidence site lattice models were proposed to interpret the intergrowth of the two SAPs. It was found that the two interfaces have nearly the same volume strain, validating the coexistence of both orientation relationships.

Magnetoelectric and HR-STEM investigations on eutectic CoFe2O4–Ba1–xSrxTiO3 composites

Multiferroic Ba1–xSrxTiO3–CoFe2O4 (x = 0.03, 0.05) composites with rarely investigated 3-3 connectivity were prepared by eutectic crystallization in an optical floating zone furnace. High-resolution scanning transmission electron microscopy investigations of the CoFe2O4–BaTiO3 interface revealed an almost perfect connection between both components. These micrographs also showed that the impact of post-annealing in air was much larger than expected and resulted in formation of small BaTiO3 inclusions in the CoFe2O4 phase. The magnetoelectric coefficient αME was studied in detail with respect to its dependence on the static magnetic field, the frequency of the driving AC-field and temperature. Furthermore, the influence of different growth rates (5, 10 and 20 mm h−1), chemical composition, sample thickness and the alignment of electrical polarization and magnetic field (collinear or vertical) on the magnetoelectric properties were studied. The largest value of αME = 1.3 mV Oe−1 cm−1 was found for a sample grown at 5 mm h−1. For even slower growth rates, a higher Sr content was required to avoid the formation of impurity phases leading to a decrease of αME.

Elastic constants of β-Ti15Mo

Elastic constants of single crystals of metastable β-titanium Ti15Mo alloy (in wt. %), grown in an optical floating zone furnace, were measured by resonant ultrasound spectroscopy with the aim to study the dependence of these constants on formation of isothermal ω particles. Samples with different heat treatment (isothermal/anisothermal ageing at different temperatures) were studied. Ultrasonic measurements were complemented by characterization of the samples by transmission electron microscopy. The results proved that isothermal ω particles always exactly follow the original cubic symmetry of the β matrix and that the evolution of the elastic constants of the β-ω multi-phase crystals and the volume fraction of ω phase can be reliably approximated using Hill's homogenizing procedure, assuming cubic elastic constants of the β phase and isotropic elastic constants representing ω particles. It was shown that ultrasonic methods can be used for the study of the evolution of microstructure of metastable β-titanium alloys due to the high contrast in elastic moduli of the β and ω phases.

Scintillation properties of RE2Hf2O7 (RE = La, Gd, Lu) single crystals prepared by xenon arc floating zone furnace

Pyrochlore La2Hf2O7, Gd2Hf2O7, and Lu2Hf2O7 single crystals were successfully grown by using an optical floating zone furnace. The synthesized crystals exhibit scintillation with a broad emission peaking around 440–510 nm. The crystal quality and luminescence intensity are sufficiently high that it is applicable for pulse height spectrum measurements. Under 241Am alpha-ray exposure, the pulse height spectrum indicates the estimated light yield of a La2Hf2O7 crystal is 270 photons/MeV.

Optimization of single crystal growth of candidate quantum spin-ice [formula omitted] by optical floating-zone method

We report the optimized conditions for growing the high quality single crystals of candidate quantum spin-ice Pr2Hf2O7 using the optical floating-zone method. Large single crystals of Pr2Hf2O7 have been grown under different growth conditions using a four-mirror type optical floating-zone furnace and their microscopic structural differences have been probed by high-resolution synchrotron X-ray diffraction (SXRD). The SXRD data reveal that the crystals grown under flowing argon (∼2 L/h) atmosphere with slightly off-stoichiometric (optimized) starting composition yields the highest quality crystals. The magnetic susceptibility, isothermal magnetization and heat capacity data of optimally grown crystals are presented.

Two fold spin reorientation and field induced phase transition in Ho0.5Dy0.5FeO3 single crystal

Magnetic measurements on oriented single crystals of Ho0.5Dy0.5FeO3 grown using optical floating zone furnace provide evidence for two spin reorientations of Fe3+ magnetic sublattice viz.,Γ4→Γ1→Γ2 at temperatures TSR1=49K and TSR2=26K. As magnetic field along c axis increases, the sample resumes Γ4 spin configuration and a large field is likely to disrupt the spin reorientation process. It is evident from isothermal magnetization along c axis that field induced Γ1→Γ4 transition is feasible within the intermediate temperature range of TSR1-TSR2 and can be triggered at a critical field. Such magnetic behavior is better understood as a consequence of anisotropic effective field, modified by the application of external magnetic field.

Effect of interfacial energy on microstructure of a directionally solidified Al2O3/YAG eutectic ceramic

AbstractAn Al2O3/Y3Al5O12 eutectic ceramic was prepared with a c‐axis sapphire seed by an optical floating zone furnace. The crystallographic relationships in the initial and the steady growth sections of the as‐grown eutectic ceramic were investigated by electron backscattering diffraction and transmission electron microscopy. The corresponding results were: &lt;111 &gt; {101}Y3Al5O12 || &lt;0001 &gt; {}Al2O3 and &lt;110 &gt; {}Y3Al5O12 || &lt; &gt; {0001}Al2O3, respectively. The steady orientation of the latter one shows smaller planar disregistry. Interfacial strain played the decisive role in affecting the solidification behavior of the Al2O3/Y3Al5O12 eutectic ceramic. The stability of interfaces with minimum interfacial strain and better ionic charge balance in irregular microstructure prevail upon the constraint of the seed. These results might cast light for the interfacial design of the Al2O3/Y3Al5O12 binary eutectic ceramic.