Scanning SQUID Microscope

Scanning SQUID microscope (SSM) is a modern technique capable of imaging a magnetic field distribution in close proximity across the surface of a sample under investigation with high sensitivity close to 200 pT and with high spatial resolution less than 50 microns. It is based on a high-transition temperature thin-film Superconducting Quantum Interference Device (SQUID) sensor. SSM is operated at liquid-nitrogen temperature and is capable to measure the cold samples that are held in the same cryogenic environment at 77 K. The SSM’s output is displayed as a false-color image of the Bz – component of magnetic field perpendicular to a sample surface versus position on the sample.

Fields of application:

  1. A scanning SQUID microscopy is very convenient technique for investigating magnetic properties of superconducting thin-film structures. This technique can be used as a powerful tool for the diagnostics of superconductor integrated circuits and highly sensitive bolometres. SSM was used to record current-induced magnetic field maps of superconductor topologies based on YBCO film structures. Images of the individual vortices trapped in the inspected film have been obtained using SSM.
  2. SSM can be applied to study magnetic properties of the ultra-thin magnetic films. Stray magnetic fields distribution producing by remnant magnetization or induced magnetization of the film can be visualized. The domain structures, orientation of the magnetic moment and value of magnetization can be determined. Images of the remnant magnetization and induced magnetization in the in-plane magnetizing field up to 5 * 104A/m of the 1 nm – 20 nm thick Ni films have been obtained using SSM.
  3. A scanning SQUID technique has the potential to image a character of distribution and determine a magnitude of a magnetic field normal component over the surface of magnetic recording media. The magnetic images of the fragments of the standard 3’1/2 floppy disks have been obtained. Fig.1 shows one of these magnetic images. The SSM space resolution achieved is 20 microns, making it impossible to resolve the single magnetic domain of recording media with less then 1micron size (one bit of information). But individual tracks with 200-microns separation are clearly seen.

Fig.1. Magnetic image of the floppy disk fragment with recorded information. The lower curve corresponds to a diagonal cross section through the upper image.

Minimum detectable field: 2 * 10-10 T.
Minimum detectable current: 10 nA with a sensor-sample separation of 50*10-3 mm.
Sensor operation temperature: 77.8 K.
Sample scanning range: 10 mm * 10 mm in X-Y directions and 1 mm in vertical direction.
Scanning step size: minimum step size in X-Y directions is about 1 micron, in depending on a task it can be adjusted from 2 microns to 100 microns.
Typical scanning speed: 0.2 mm per second.
Scanning technique: system is operated in a computer driven mode.