High temperature superconductor dc-SQUID microscope with a soft magnetic flux guide

Abstract

A scanning SQUID microscope based on high-temperature superconductor (HTS) dc-SQUIDs was developed. An extremely soft magnetic amorphous foil was used to guide the flux from room temperature samples to the liquid-nitrogen-cooled SQUID sensor and back. The flux guide passes through the pick-up loop of the HTS SQUID, providing an improved coupling of magnetic flux of the object to the SQUID. The device measures the z component (direction perpendicular to the sample surface) of the stray field of the sample, which is rastered with submicron precision in the x-y direction by a motorized computer-controlled scanning stage. A lateral resolution better than 10 µm, with a field resolution of about 0.6 nT Hz −1/2 was achieved for the determination of the position of the current carrying thin wires. The presence of the soft magnetic foil did not significantly increase the flux noise of the SQUID.

Superconducting Quantum Interferometers for Nondestructive Evaluation

“…The high-T c DC SQUID microscope developed at FZJ for studies of room temperature objects is based on a high-T c DC SQUID with a magnetic flux antenna and was described in detail in our previous publications [48,49,50] (see Figure 6). Here, we review it briefly, report new results obtained with the system and provide an outlook for further developments.…”

Linear magnetic flux amplifier

“…Recently, π/2-and π-SQUIDs based on d-wave superconductors have been investigated as the possible candidates for SQUIDs without the external flux bias [4,5,6]. Soft ferromagnetic materials have been used as another means to improve the sensitivity of SQUID magnetometers [7,8,9]. Even though soft ferromagnets provide an enhancement of sensitivity, they are generally considered unfavorable because magnetization switching, domain wall nucleation and motion, as well as additionally generated vortices can substantially increase the noise.…”

Epitaxial Oxide Heterostructures for Ultimate High-Tc Quantum Interferometers

“…These requests, in turn, supported the further development of high-T c sensors: more than 20 types of high-T c DC SQUID magnetometers and gradiometers prepared by the high oxygen pressure sputtering technique are now available from Forschungszentrum Jülich GmbH. The epitaxial oxide heterostructures were used in different types of SQUID microscopes ) (Poppe et al, 2004); in a SQUID monitor for measuring the beam current of accelerator radioisotope ions (Watanabe et al, 2004(Watanabe et al, , 2010; for geomagnetic surveys (Chwala et al, 1999, Clem et al, 2001, Fagaly, 2006; for non-contact testing of semiconductor structures with a SQUID laser microscope (Daibo et al, 2002(Daibo et al, , 2005; in the NDE systems for eddy current testing of aircraft wheels and rivets (Grüneklee et al, 1997); for magnetic inspection of prestressed concrete bridges (Krause et al, 2002); for picovoltmeters (Faley et al, 1997b); and for the localization and identification of deep-seated artificial defects such as holes, slots and cracks in multilayer reinforced carbon fibre polymer panels by eddy current SQUID NDE (Valentino et al, 2002) and for magnetocardiography (MCG) measurements (Drung et al, 1995;Faley et al, 2002). Biomagnetic measurements are among those general-purpose applications for which the SQUID measurement systems are preferred due to their sensitivity and ability to measure vector components of magnetic fields.…”