Guihuan Du

Synthesis of magnetite nanoparticles in W/O microemulsion

huazhong univ sci & technol, dept phys, wuhan 430074, peoples r china. huazhong univ sci & technol, state key lab laser technol, wuhan 430074, peoples r china. chinese acad sci, int ctr mat phys, shenyang 110015, peoples r china. tongji med coll, wuhan 430030, peoples r china.;liu, zl (reprint author), huazhong univ sci & technol, dept phys, wuhan 430074, peoples r china;wangxin207@sohu.com klyao@hust.edu.cn

Electric properties of BiFeO3 films deposited on LaNiO3 by sol-gel process

Sol-gel process was adopted to prepare BiFeO3 films. Pure phase BiFeO3 films were deposited on LaNiO3 coated Si (111) substrates at various annealing temperatures of 450–600°C. The films annealed at 450–600°C are (110) and (110) biaxis preferential oriented. Below 550°C, the remnant polarization increases with the annealed temperature. The film annealed at 550°C has the largest double remnant polarization of 12.8μC∕cm2. For the film annealed at 600°C, small double remnant polarization of 2Pr=4.6μC∕cm2 was observed for its low breakdown electric field. Besides, the electric property is enhanced with the annealing temperature below 550°C and it is deteriorated for the film annealed at 600°C. Large dielectric constant and low leakage conduction were obtained by the improvement of preparation technology.

The influence of high magnetic field on electric-dipole emission spectra of Eu3+ in different single crystals

In this work, the effect of pulsed high magnetic field on the integral intensity of the electric-dipole emission spectrum of Eu3+ in YVO4:Eu3+ and GdVO4:Eu3+ single crystals was studied and the results showed magnetic field induced luminescence suppression in YVO4:Eu3+ and luminescence expansion in GdVO4:Eu3+. The single crystals were prepared by the optical floating zone method. The strong effect of the magnetic field on the splitting and emission of 5D0–7F2 and 5D0–7F4 transitions in Eu3+ was investigated. The integral luminescence intensities of Eu3+ are proportional to the magnetic field at higher than 15 T. For GdVO4:Eu3+, the integral intensity increases with the strengthening of magnetic field, and is completely opposite to that for YVO4:Eu3+. In this study, the dependence of luminescence integral intensity on the magnetic field was proposed to be the result of the structural change induced by high magnetic field which changes the symmetry of Eu3+ ions in single crystals.

Magnetic field induced great photoluminescence enhancement in an Er 3+ :YVO 4 single crystal used for high magnetic field calibration

An optical technique is proposed for the accurate calibration of pulsed high magnetic fields utilizing the magnetic field dependent photoluminescence (PL) properties in an Er(3+):YVO(4) single crystal at 80 K. Bright green PL emissions are excited by a 487.5 nm laser line and can be enhanced greatly by a magnetic field at certain field values (B(c)). Since the B(c)s under 10 T are extremely stable for a given sample at a certain temperature, and the FWHM of the enhancement peaks are less than 0.9 T, an Er(3+):YVO(4) single crystal is proven to be a good candidate for pulsed high magnetic field calibration. The detailed processes and numerous advantages of the technique are presented in this work.

Effect of Ce3+ dopant ions on the shape and luminescence of YPO4:Eu3+ and YPO4:Tb3+ nanocrystals

Nanoparticles of YPO4:Eu3+, YPO4:Eu3+:Ce3+, YPO4:Tb3+, and YPO4:Ce3+:Tb3+ with different amount of Eu3+ or Tb3+ dopant ions were synthesized by a hydrothermal route. Particle structures and morphologies were investigated and it was found that the increase of Eu3+ or Tb3+ ions, and co-doping with Ce3+ ions resulted in a transition of the crystal structure from tetragonal to hexagonal phase. The phase transition and the morphology transformation should be ascribed to the change of the average radius of cation by doping Ce3+, or to the changing the amount of Eu3+ or Tb3+. The energy transfer from Ce3+ ions to Eu3+ and Tb3+ ions was tested by studying the photoluminescence lifetime of YPO4:Eu3+, YPO4:Eu3+:Ce3+, YPO4:Tb3+, and YPO4:Ce3+:Tb3+ nanoparticles, and their energy transfer results in the improvement of the luminescence intensity. A schematic diagram for the electronic transitions of the studied systems is presented.

Quantum correlation and phase transitions in a two-dimensional doubly decorated Ising-Heisenberg model

We investigate the pairwise quantum correlation, characterized by quantum entanglement (QE) and quantum discord (QD), of a two-dimensional Ising-Heisenberg model on a planar doubly decorated lattice. At zero temperature, the concurrence (a measurement of pairwise entanglement) and the QD are related to the correlation function qxx and the staggered magnetization δSz, respectively, and both of them indicate the quantum phase transition (QPT) of the system. However, in a finite-temperature phase transition, all the pairwise entanglement vanishes thus it fails to detect the critical temperature TC, while the derivative of QD diverges at TC. This shows clearly that QD can capture the signal of phase transition in a separable state, thus it has a broader scope of application than QE in detecting phase transitions.

Hidden local symmetry of Eu3+ in xenotime-like crystals revealed by high magnetic fields

The excellent optical properties of europium-doped crystals in visible and near infrared wavelength regions enable them to have broad applications in optoelectronics, laser crystals and sensing devices. The local site crystal fields can affect the intensities and peak positions of the photo-emission lines strongly, but they are usually difficult to be clarified due to magnetically degenerate 4f electronic levels coupling with the crystal fields. Here, we provide an effective way to explore the hidden local symmetry of the Eu3+ sites in different hosts by taking photoluminescence measurements under pulsed high magnetic fields up to 46 T. The zero-field photoluminescence peaks split further at high magnetic fields when the Zeeman splitting energy is comparable to or larger than that of the crystal field induced zero-field splitting. In particular, a magnetic field induced crossover of the local crystal fields has been observed in the GdVO4:Eu3+ crystal, which resulted from the alignment of Gd3+ magnetic mom...

Spin reorientation and spin-flop transition in multiferroic manganites Y1–xTbxMnO3 (x = 0, 0.1, 0.2) single crystals

We investigated the structure and magnetic properties of the multiferroic hexagonal manganite Y1−xTbxMnO3 (x = 0, 0.1, 0.2) single crystals. At 23 K, a Mn spin reorientation transition, which is not reported in the parent compound YMnO3, is observed in Y0.8Tb0.2MnO3. At a lower temperature, another new transition is observed in the doping system, which is attributed to the formation of long range antiferromagntic order of the doped Tb3+ moments. Based on the experimental results, we suggest that the effect of Tb doping is to bring about the increase of the Mn-O-Mn bond angle and the relief of the magnetic frustration. With increasing the doping level, for x = 0.2, when a magnetic field is applied parallel to the c axis, the field induced spin-flop transition is appeared, which indicates the reorientation of the Mn3+ moments along with the field-induced ferromagnetic ordering of the Tb3+ moments. These results suggest that the possibility of the Tb doping can change the magnetic structure and ferroelectric...