Search

The magnetocaloric applicability of the perovskite-structured (Pr,Ca) manganite family (PCMO) was estimated based on the magnetic transition entropies of polycrystalline bulk samples. Transitions in the temperature range from 5 to 400 K were investigated in external fields up to 5 T. Earlier results published on the matter were reproduced, extended to Ca concentrations below $x = 0.2$ and up to $x = 1$ , and complemented by determining standardized refrigerant capacity estimates corresponding to the largest entropy changes detected in each sample. The quantitative agreement between the measured transition entropies and literature also served to verify a time-optimized data collection method based on quick temperature scans of magnetization at constant magnetic fields. Making use of the mathematical regularity of magnetization curves, improved time, and cryogen efficiency was arguably attained compared with a more traditional data collection method without significant loss of accuracy. The results of this paper convey a very graphical overview of the quite well established phase diagram of PCMO and promise a significant magnetocaloric effect below 150 K, possibly on par with that exhibited by Gd-based alloys around room temperature. However, little hope can be offered for the room temperature refrigeration applications of PCMO. [ABSTRACT FROM AUTHOR]

The accommodation field, B*, is generally defined to be the field at which the cross over from single vortex pinning to collective pinning occurs. It is determined from magnetization curves as the point where the Jc plateau ends and it used as a convenient way of comparing the pinning properties of superconducting films. Similarly, the characteristic field, Bc, can be obtained from magneto-optical (MO) images from when the flux fronts meet in the middle of the film. The matching field, Bc at which there is one vortex line per pinning site, is sometimes thought to be the same as B*, but in BaZrO3-doped YBa2Cu3O7 films the calculated BΦ, is much higher than the observed B*. BΦ, can be determined from angular dependent transport measurements. All of the field values correspond to some special case in the flux pinning in the film and relate to Jc. In this work we have determined Bc, B * and BΦ, for different kinds of YBCO films using MO, magnetization and transport measurements to reveal the deeper meaning of the special fields. [ABSTRACT FROM AUTHOR]

We report the effect of 4 wt% BZO-doping in GdBCO thin films on (100) STO substrates with novel nanograined target materials deposited by pulsed laser deposition (PLD) method. X-ray diffraction, atomic force microscopy and magnetization measurements, which were made in particularly wide temperature and magnetic field range, were used to determine the structural and superconducting properties. The results were compared with ones of YBCO. The deposition temperature, Ts, is not very critical for GdBCO and it is found to be much lower in undoped and BZO-doped GdBCO than in YBCO. The BZO-doping of GdBCO enhanced the field dependence of critical current density, jc, at low temperatures. Furthermore, BZO-doping enhances the accommodation field, B*, below 60 K being clearly higher at 10 K in doped GdBCO than in YBCO. The pinning mechanism in GdBCO was concluded to be similar to that of YBCO. Our results clearly show that undoped and BZO-doped nanophase GdBCO is a very promising target material for applications as well as for coated conductors. [ABSTRACT FROM AUTHOR]

Superconducting YBa2Cu3O6+x (YBCO) films are grown by pulsed laser deposition (PLD) in the orientation where its c-axis is lying in the plane of the film using (110) oriented SrTiO3 (STO) substrates with PrBCO template layer. By optimization of deposition temperature and rate the easily formed (103) orientation was avoided to get smooth and completely (110) oriented YBCO films. To improve the superconducting properties, we have also optimized the BaZrO3 (BZO)-doping in the (110) YBCO films. This gives the possibility to apply the current along the YBCO CuO2 planes where the critical current is much higher in thin film multilayers or to investigate the anisotropy and the effect of BZO pinning structure in different film orientations. [ABSTRACT FROM AUTHOR]

Studies thermally induced motion and clustering of single particles obtained by pulsed laser deposition (PLD) from uniform size Y-Ba-Cu-O superconducting thin films. Average height and radius of particles after annealing at different temperatures; Dependence of the average height and radius of the particles on temperature.

We have prepared YBCO nanopowder by the sol-gel route. The original powder contains weak links as observed by magnetization and microwave absorption measurements. Most of the weak links could be reduced by keeping the powder in ethanol for 30 min in an ultrasonic bath. It was also found that the ultrasonic bath does not affect the superconducting properties of the nanoparticles themselves. The modulation field applied in the microwave absorption measurements was found to have a large effect on the temperature dependence of the absorption. This phenomenon was explained with a phase diagram for the weak links. [ABSTRACT FROM AUTHOR]