Magnetic granularity in pulsed laser deposited YBCO films on technical templates at 5 K

Abstract

The manifestation of granularity in the superconducting properties of pulsed laser deposited YBCO films on commercially available metallic templates was investigated by scanning Hall probe microscopy at 5 K and was related to local orientation mapping of the YBCO layer. The YBCO films on stainless steel templates with a textured buffer layer of yttrium stabilized ZrO2 grown by alternating beam assisted deposition have a mean grain size of less than with a sharp texture. This results in a homogeneous trapped field profile and spatial distribution of the current density. On the other hand, YBCO films on biaxially textured NiW substrates show magnetic granularity that persists down to a temperature of 5 K and up to an applied magnetic field of 4 T. The origin of the granular field profile is directly correlated to the microstructural properties of the YBCO layer adopted from the granular NiW substrate which leads to a spatially inhomogeneous current density. Grain-to-grain in-plane tilts lead to grain boundaries that obstruct the current while out-of-plane tilts mainly affect the grain properties, resulting in areas with low . Hence, not all grain boundaries cause detrimental effects on since the orientation of individual NiW grains also contributes to observed inhomogeneity and granularity.

Effect of Silver Doping on the Superconducting and Structural Properties of YBCO Films Grown by PLD on Different Templates

“…At the same time, scanning Hall probe microscopy (SHPM) provided additional information on the local distribution of the critical current density. Similar studies have been performed previously on pure YBCO layers grown on metallic templates [ 23 , 24 , 25 ].…”

Manifestation of granularity in the transport current of coated conductors

“…The spatial homogeneity of the superconducting properties was imaged using SHPM. The setup consists of a Hall effect sensor with a piezo-positioning system [8,9]. Magnetic field profiles were recorded in a He-gas flow cryostat where the temperature can be stabilized between 3 K and 300 K with a spatial resolution of 5 μm.…”

“…Two types of commercially available templates are typically used: a rolling-assisted biaxially textured substrate (RABiTS) made from NiW alloys and Hastelloy or stainless steel tapes with a textured buffer layer prepared by ion-beam assisted deposition or inclined substrate deposition. Various studies have shown that RABiTS tapes have large grains of usually more than 20 μm, which are transferred to the deposited REBCO layer [2,6,7].…”

Strongly Enhanced Growth of High-Temperature Superconducting Films on an Advanced Metallic Template

“…Until now, mainly YBa 2 Cu 3 O 6+ x (YBCO) and GdBa 2 Cu 3 O 6+ x (GdBCO) has managed to grow on these buffered metallic templates utilizing PLD for the large-scale coated conductor manufacturing . However, these nonsingle crystalline templates are extremely harsh growth environments for the films to be deposited due to the presence of the great number of grain boundaries, which are usually transferred on the film deposited on the top of it. − This grain boundary transfer significantly diminishes the benefits of the HTS materials, such as liquid nitrogen cooling, as they limit the superconducting critial current more substantially in the high temperature range. The critical current, determined by the grain boundaries, has been observed to decrease linearly in zero field as the temperature is increased according to the superconductor–insulator–superconductor (SIS) model. − More unfortunately, under applied magnetic fields the critical current is suppressed exponentially as a function of temperature, and in some cases the grain boundaries can even become weak links blocking the applied current completely. , …”