A scanning SQUID microscope was used to image vortex trapping as a function of the magnetic induction during cooling in thin-film YBa2Cu3O 7−δ (YBCO) strips for strip widths W from 2 to 50 µm. We found that vortices were excluded from the strips when the induction Ba was below a critical induction Bc. We present a simple model for the vortex exclusion process which takes into account the vortex -antivortex pair production energy as well as the vortex Meissner and self-energies. This model predicts that the real density n of trapped vortices is given by n = (Ba − BK )/Φ0 with BK = 1.65Φ0/W 2 and Φ0 = h/2e the superconducting flux quantum. This prediction is in good agreement with our experiments on YBCO, as well as with previous experiments on thin-film strips of niobium. We also report on the positions of the trapped vortices. We found that at low densities the vortices were trapped in a single row near the centers of the strips, with the relative intervortex spacing distribution width decreasing as the vortex density increased, a sign of longitudinal ordering. The critical induction for two rows forming in the 35 µm wide strip was (2.89 + 1.91 − 0.93)Bc, consistent with a numerical prediction.

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Sandwich structures of gold−self-assembled monolayer−gold were prepared by deposition of gold on alkylthiolate self-assembled monolayers on polycrystalline gold, using pulsed laser deposition (PLD) through a nanosieve. The arrays of sandwiches, around 600 nm in diameter, approximately 10 nm high, and spaced 1.6 μm apart, were analyzed using tapping mode atomic force microscopy. Electrochemical copper deposition experiments showed that of the islands deposited on octadecanethiolate monolayers about 15% were electrically insulated from the bottom gold electrode. This means that PLD is a suitable technique for the fabrication of metal−SAM−metal sandwich structures.

Pulsed laser ablation (PLA) has been used to grow barium ferrite films on AlzQ3 single crystal substrates. When deposition occurs in an oxidising atmosphere at high temperatures, the films are single BaFelz019 phase with very well orientation following the (001) texture, and exhibit a large perpendicular magnetic anisotropy. In this case, the microstructure and the anisotropy orientation are not influenced by variation of the oxygen pressure in the range 20-530 mtorr, but the coercivity and the remanence are affected. Films prepared without oxygen, are isotropic. XRD measurements reveal the absence of the BaFelzQp~ which becomes unstable. On the other hand, the presence of other phases as Ba2FehO1l and Fez03 is detected. The annealing study reveals the presence of the threshold temperature (620°C) for the appearance of the magnetisation and the anisotropy orientation. This temperature also corresponds to the onset in growth of the crystalline structure of barium ferrite. In the latter case, the coercivity was found to be greatly reduced by the increase in grain size at higher annealing tempera turesZndex T e r m -Ba -Ferrite, Laser Ablation, Perpendicular Anisotropy, Annealing

Quasiparticle (QP) injection devices based on HTS could play an important role in future superconducting applications if material aspects can be better controlled. One reason why this kind of device received little attention in the past is the lack of an appropriate barrier for QP tunnelling. In a series of experiments, we used different barriers to test if they are suitable, i. e. if a current and possibly a voltage gain can be achieved. We improved the performance of planar YBCOhatural barrierlAu devices and a current gain of more than 6 at 40K was observed. Most devices, however, showed signs of heating effects. Another barrier material was SrTiQ, with layers of 5 -6 nm thickness. Current-voltage characteristics showed that the barriers were continuous and we observed current gains of up to 3 at 60 K. PrBa2Cu3O7., is an interesting candidate if one could overcome the problem of resonant inelastic tunnelling for QP. In a series of experiments we demonstrated that, even for 3 nm thin PBCO barriers on a-and c-axis oriented YBazCus07.,, most devices showed at best a current gain of 1. However, we have indications that a current gain of 10 could be possible with unity voltage gain.