High resolution magnetic microscopy using a DC SQUID

Abstract

Using a 4.2K Nb-PbIn dc SQUID with a 60 pm inner hole side length, we have constructed a novel 1-D magnetic flux microscope with an unprecedented combination of spatial and magnetic field resolutions. During imaging, the sample is moved past the SQUID at a separation of about 38 pm and the output from the SQUID is recorded as a function of the sample position. The system achieves a spatial resolution of about 66 pm and a magnetic field resolution of about 5.2 pTHz-lD at a frequency of 6 kHz. We have used the microscope to obtain susceptibility images of patterned superconducting samples in low fields and have devised a simple method for measuring static magnetic fields. by no more than a distance diamagnetism causes mag feedback and field coils. 1051-8223/93$03.00 0 1993 IEEE This work was supported by the State of Maryland through the Center for Superconductivity Research. We thank E. Knouse for loan of the stepper motor and controller and J. Clarke for the design of the feedback electronics. Manuscript received August 24,1992.

Grain boundaries in high-Tcsuperconductors

“…Grain-boundary-junction-based high-T c SQUIDs are further implemented in systems for nondestructive evaluation, e.g., of aircraft parts (Hohmann et al, 1997;Krause et al, 1997;Kreutzbruck et al, 1997;Mü ck et al, 1997) or reinforcing rods in concrete structures, for the detection of fine magnetic particles in copper wire (Nagaishi et al, 1997), in biology, and for geophysical surveying. Scanning SQUID microscopy is an enticing extension of these applications (see, for example, Mathai et al, 1992Mathai et al, , 1993Kirtley et al, 1994), which in high-T c versions employing bicrystal grain-boundary junctions was introduced by the groups of Wellstood at the University of Maryland (Black et al, 1993) and of Clarke at UC Berkeley (T. S. Lee et al, , 1997. Even though these microscopes are based on cryogenic sensors, they allow investigations of samples kept at room temperature.…”

Experimental Proof of a Time-Reversal-Invariant Order Parameter with aπshift inYBa2Cu3Mathai1, Gim2, Black3 et al. 1995Phys. Rev. Lett.Self Cite2504920View full textAdd to dashboardCite

“…To begin a measurement, we first use the SQUID microscope to determine the static magnetic field [14] and then use a field coil to null the field to better than &bp/10 in the sample SQUIDs. We next take magnetic images of the sample and, if trapped flux is found, thermally cycle the sample until all the flux is gone.…”

Scanning Squid Microscopy

“…The capabilities of systems with cryogenic samples is even more impressive. SQUID microscopes have been demonstrated with a spatial resolution as fine as 4 µm for samples that are in the same cryogenic environment as the SQUID sensor (14,16,(38)(39)(40)(41)(42)(43)(44). Systems with both the sample and the SQUID immersed in liquid helium have 66 µm resolution and 5.2 pT/ √ Hz noise at 6 kHz (42), and 10 µm at 100 pT/ √ Hz (43); the Conductus Scanning Magnetic Microscope TM provided micron resolution for helium-temperature samples (38).…”