Itsuhiro Fujii

Transport critical currents and flux pinning mechanisms in single-crystalline thin films of YBa2Cu3O7−δ

Abstract In order to investigate the anisotropy of transport critical current densities J c and flux pinning properties, we have measured J c for YBa 2 Cu 3 O 7-δ single-crystalline thin films in magnetic fields H up to 12 T as a function of the angle between H and the crystal axes. The observed angular dependence of J c at 77 K and near 1.0 T could be explained by the model of intrinsic flux pinning proposed by Tachiki and Takahashi under the condition of transport current I ⊥ H . However, in a high field region near the upper critical field H c2 , the results disagreed with this model. We found that the reduced field H / H c2 dependence of the volume pinning force F p could be represented by F p ∝ ( H / H c2 ) 1 2 (1- H / H c2 ) 2 for all configurations for which we measured. The results indicate that both intrinsic and extrinsic pinning centers worked as a surface-type (two-dimensional) pinning. Furthermore, the angular dependence of H c2 was explained by the effective mass model.

Influence of Rare Earth Ions on BaO-TiO2-Rare Earth Oxide Ceramics for Microwave Applications

The dielectric ceramic materials, 0.143BaO-0.714TiO2-0.143 rare earth oxides (REOx), have unique dielectric properties at microwave frequencies, which depend on the rare earth element (RE=Pr, Nd, Sm). In order to study the effect of the rare earth ions on dielectric properties, infrared reflection spectra of these ceramics were measured from 50 to 4000 cm-1 at room temperature. These data were analyzed according to the model proposed by Gervais and Piriou. Also, the fourth-order dielectric constants of these materials were estimated for the purpose of investigating the relationship between the dielectric loss and the anharmonic terms in the potential energy.

Preparation of low-temperature Li3VO4 single crystal by floating zone technique

Abstract Single crystals of the low temperature phase β II Li 3 VO 4 were prepared by using a floating zone technique. Three problems, micro-cracks, accumulation of bubbles and the coloration of crystals, were faced during single crystal growth. These problems were investigated in relation with the initial molten zone composition, gas atmosphere and the purity of starting materials, respectively. The obtained crack-free, colorless and transparent β II Li 3 VO 4 single crystal had a diameter of 5 mm and was 5 mm long.

Magneto-optical Faraday effect of porous films comprised of cobalt-substituted barium ferrite fine particles dispersed in a resin

The magneto‐optical Faraday effect of porous films comprised of cobalt‐substituted barium ferrite (Co:BaM) fine particles fixed by a resin was investigated. The films were prepared by spin‐on process of a magnetic ink involving Co:BaM particles on glass substrates. Porous films were formed when the particle concentration of the ink, f, was low, i.e., f<0.3, and the coated ink was dried while applying a dc magnetic field normal to the substrate plane. The pit size became bigger when the coated ink was thicker, or the field was stronger. The Faraday effect of the films underwent a drastic change caused by the formation of a porous structure. The Faraday rotation spectrum exhibited dispersion‐type behavior and its center wavelength was shifted toward longer wavelength with increasing pit dimension. Rotation angle enhancement was observed, which is considered to be caused by the mode modulation of light due to the existence of the pits.

New types of SHG material, Li3VO4 and Li3PO4-type crystals

Abstract Some vanadate materials were investigated as second harmonic generation (SHG) materials for Nd: YAG lasers. Li 3 VO 4 and its derivative crystals, Li 2 ZnSiO 4 and Li 2 MgGeO 4 , were found as a new type of SHG crystal. Their crystal structure belongs to the Li 3 PO 4 type, which is formed of only MO 4 (M is Li, Zn, Si, Ge, V) oxygen tetrahedra. The SHG coefficients, d ij , of the Li 3 VO 4 single crystal was measured by the Maker fringe method and the non-linear coefficient was found to be of the same order as that of KTiOPO 4 . The origin of SHG in Li 3 VO 4 was discussed from its electronic and crystal structure. The covalency of Li 3 VO 4 is important for SHG and, further, the distorted and parallel oriented VO 4 tetrahedra enhance the SHG coefficient.

New Types of Nonlinear Optical Materials: Li3VO4- and Li3PO4-Type Structures

Li3VO4- and Li3PO4-type structure crystals are found as new types of nonlinear optical materials for second-harmonic generation (SHG). Their lattices are formed of only the MO4 oxygen tetrahedra, being different from other typical nonlinear optical materials that have previously been developed.

Anisotropy of transport critical currents and intrinsic pinning properties in YBa2Cu3O7-δ single-crystal thin films

Abstract We have studied the anisotropy of transport critical current densities J c and pinning properties for YBa 2 Cu 3 O 7−δ single-crystal thin films in magnetic fields H up to 12 T as a function of angle between H and the crystal axes. The observed angular dependence of J c agreed with the intrinsic pinning model below 2.0T at 77K. Flux pinning scaling law indicated that both intrinsic and extrinsic pinning are classified as surface type pinning.

Transport Critical Currents of Single-Crystal YBa2Cu3O7-δ Thin Films in Weak Magnetic Fields Applied at Varied Angles to Film Surface

The transport critical current density Jc of single-crystal YBa2Cu3O7-δ thin films has been measured in weak magnetic fields applied at varied angles to the film surface. There are samples with the hysteresis of Jc against H and with no hysteresis. The hysteresis occurs in fields not parallel to the direction of the transport current except near the critical temperature. The presence of the hysteresis is related to the value and the temperature dependence of electrical resistivity.

Sound Attenuation Peak Around 1 K in 3He–4He Mixtures

Sound attenuation peaks around 1 K have been measured at 10, 30 and 50 MHz in 3He–4He mixtures of the 3He concentration x3=0.013, 0.029 and 0.050 under the saturated vapor pressure. The relaxation time related to the interaction between phonons and 3He quasiparticles has been determined experimentally, and its temperature and 3He concentration dependences agree with the theory of Khalatnikov and Zharkov.

Ultrasonic Measurements Under Extreme Conditions. Part I. –Measurements at Ultralow Temperatures.

With an emphasis on technical aspects, a description is given of an example of ultrasonic measurement at ultralow temperatures.