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SPM: Scanning SQUID Microscope

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A scanning Superconducting Quantum Interference Device (SQUID) Microscope images magnetic fields above a sample surface. It has the advantages of high magnetic field sensitivity and an easily calibrated, linear response with the modest spatial resolution and the requirement of a cooled SQUID sensor. The user facility instrument at Stanford is a modification of Attocube’s cryogenic magnetic force microscope. It has a spatial resolution of between 1 and 10 microns, depending on the SQUID sensor mounted. The sample temperature can be varied between 4.3 K and 110 K while scanning. There are three imaging modes available: magnetometry, susceptometry, and current imaging. In magnetometry, magnetic fields of a few nanoTesla and dipole moments of a few hundred Bohr magnetons can be detected with a signal to noise of 1 in a 1 Hz bandwidth. Similarly, in susceptibility mode a volume susceptibility of a few times 10-7, and in current sensing mode a current of a few nano amps can be detected. The user facility SSM is in principle a fast turnaround system. 2 days should be allowed to align, cool, and run a sample. An area of the sample 5 mm by 5 mm can be accessed in a particular cooldown. Individual areas of 100 microns by 100 microns can be scanned in a particular image. Multiple scans can be merged to image larger areas.

Contact Information

Huiyuan Man

Research Examples

Scanning SQUID susceptometry images of the diamagnetic shielding of a mixture of ceramic oxides, some of which are superconducting, as a function of temperature (from M. Iranmanesh et al., Chem. Eur. J. 20 (2014) 15816-15823)
Optical image (a), and SQUID microscope image (b) of the magnetic fields directly above a natural sand sample (from J.O. Walbrecker et al., J. Mag. Resonance 242 (2014) 10-17)

Getting Started and Training Information

In order to become a qualified user on the Scanning SQUID Microscope, you need to follow each of these steps in the order as listed here:

  1. Complete the process to become a lab member of SNSF and follow the instructions to activate a Badger account.
  2. Send an email to Huiyuan Man to request training.

Basic training for SPM requires one 2-hour group session followed by a second, one-on-one session, ideally with the trainee’s own sample. Those interested in training should contact the SPM lab managers to make an appointment. Additional training in specific SPM techniques will be available on as as-needed basis following completion of the basic training.