Abstract
We show a simple and effective way to improve the vortex irreversibility line up to very high magnetic fields (60T) by increasing the density of second phase BaZrO3 nanoparticles. (Y0.77,Gd0.23)Ba2Cu3Oy films were grown on metal substrates with different concentration of BaZrO3 nanoparticles by the metal organic deposition method. We find that upon increase of the BaZrO3 concentration, the nanoparticle size remains constant but the twin-boundary density increases. Up to the highest nanoparticle concentration (n ~ 1.3 × 1022/m3), the irreversibility field (Hirr) continues to increase with no sign of saturation up to 60 T, although the vortices vastly outnumber pinning centers. We find extremely high Hirr, namely Hirr = 30 T (H||45°) and 24 T (H||c) at 65 K and 58 T (H||45°) and 45 T (H||c) at 50K. The difference in pinning landscape shifts the vortex solid-liquid transition upwards, increasing the vortex region useful for power applications, while keeping the upper critical field, critical temperature and electronic mass anisotropy unchanged.
Highlights
Simple argument that once the pinning centers have been outnumbered by vortices, their effect on increasing Hirr decreases or may even be washed out
We find that the use of (Y,Gd)BCO is beneficial and that the addition of BZO NPs does not degrade the general properties, and increases twin boundary density
At high fields we obtain a constant improvement of 25% with respect to YBCO films
Summary
Simple argument that once the pinning centers have been outnumbered by vortices, their effect on increasing Hirr decreases or may even be washed out. This idea overlooks the fact that vortices are interacting elastic objects, which form a lattice with different degrees of order depending on the underlying pinning landscape. We show that the combination of planar twin boundaries (TBs) and a higher density of three dimensional (3D) nanoparticles (NPs) increases Hirr at up to 60 T. In the case of TBs there is a clear signature of the matching field at very low fields (0.5 T) but their presence continues to increase Hirr up to 60 T. We find no signs of saturation in the improvement of Hirr up to 3 wt% BaZrO3 (BZO) added to REBCO wire up to the highest field measured (60 T), and obtain record high values
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