Skip navigation

SPM: Scanning SQUID Microscope

Overview

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, and the disadvantages of 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 4.2K and 150K 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 1Hz bandwidth. Similarly, in susceptibility mode a volume susceptibility of a few times 10<sup>-7</sup>, and in current sensing mode a current of a few nano amps can be detected. Although the user facility SSM is in principle a fast turnaround system, in practice at least 2 days should be allowed to align, cool, and run a sample. An area of the sample 2.5mm by 2.5mm can be accessed in a particular cooldown. Individual areas of up to 150 microns by 150 microns can be scanned in a particular image. Multiple scans can be merged to image larger areas.

 

Contact Information

John Kirtley
(650) 492-5090

 

Getting Started

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.

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

 

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)