Magnetic microscopy using a liquid nitrogen cooled YBa2Cu3O7 superconducting quantum interference device

Abstract

We have developed a magnetic flux microscope which uses a liquid nitrogen cooled thin-film YBa2Cu3O7 dc superconducting quantum interference device (SQUID) to produce two-dimensional images of magnetic fields. The instrument operates as a scanning probe microscope with a spatial resolution of about 80 μm and a field of view of about 100 mm2. The equivalent magnetic field noise in the SQUID ranges from 80 pT Hz−1/2 at 1 Hz to 20 pT Hz−1/2 at 1 kHz, yielding a field resolution of about 200 pT in our images. We have used the microscope to image magnetic domains in ferromagnetic samples, small currents flowing in fine wires, and trapped flux and diamagnetic susceptibility in superconducting thin films.

Antiferromagnetic ordering in arrays of superconductingπ-rings

“…18,19,20,21 The SQUID microscope images shown here were made at a temperature of T < 5K, with the sample cooled and imaged in the same fields. The size of the pickup loop used will be indicated for each image.…”

Cold SQUIDs and hot samples

“…Examples of the use of cold sample microscopy at helium temperatures include the study of vortex structure and dynamics in superconducting networks and clusters [27] and the determination of the pairing symmetry in high-Tc superconductors [28,29,30]. Black and co-workers have pioneered the use of high-Tc SQUIDs operated at liquid nitrogen temperature to examine cold samples with a variety of techniques, including static magnetization [31], eddy current [32], radio frequency [33], and microwave imaging [34]. Low-Tc SQUID microscopes have been used extensively for nondestructive evaluation (NDE) of warm samples in many different modes [26], and a number of different systems have been described [35,36,37,38].…”

High‐resolution imaging using a high‐Tc superconducting quantum interference device (SQUID) magnetometer

“…Recently developed superconducting quantum interference device (SQUID) magnetometers are extremely sensitive and are able to measure planar structures with a field sensitivity of 200 pT at a resolution as low as 80 gm [Black et al, 1993]. SQUID magnetometers therefore fill a gap between traditional paleomagnetic sample measurements and microscope techniques and may be used for mapping continuously structures in the millimeter range.…”