Researchers from the SNI network have developed innovative, extremely small, and robust magnetic field probes that enable high-resolution images of nanoscale magnetic structures. The sensors are based on superconducting quantum interference devices (SQUIDs) – superconducting components that are among the most sensitive magnetometers precisely detecting even very weak magnetic fields.

Highly sensitive imaging of magnetic fields shows how currents, spins, and magnetic structures actually function inside materials. The data provide the basis for the development of modern technologies such as superconductivity, quantum computing and novel data storage.

Among the most sensitive magnetic field sensors are superconducting quantum interference devices, or SQUIDs for short. They are based on superconductivity and can measure even extremely weak magnetic signals – far better than conventional methods. 

SQUIDs at the tip of cantilevers
Researchers from the Universities of Basel and Tübingen have now developed novel SQUID probes with unprecedented resolution, as reported in the journal Physical Review Applied. Using a combination of optical lithography and precise focused ion beam processing, they fabricated SQUIDs from niobium with internal structures of around 10 nanometers directly at the tip of silicon cantilevers.

“The cantilever serves as a support structure that allows the SQUID probe to be brought very close to the surface to scan the magnetic field locally,” explains Argovia Professor Martino Poggio from the Department of Physics and Swiss Nanoscience Institute at the University of Basel. “At low temperatures, we were able to achieve magnetic field imaging with a resolution of less than 100 nanometers.”

Through additional nanostructuring with neon or helium ions, the team was able to integrate further functions – for example, a modulation line for control of the magnetic flux or a third Josephson contact for extending the magnetic field range, in which the probe is sensitive. This combination of high control, robustness, and fine spatial resolution significantly expands the range of applications for SQUID scanning microscopy – from magnetic materials and superconducting systems to samples used in quantum computing.

Investigation of complex systems possible
As a proof-of-principle, the researchers demonstrated the performance capabilities of the new probes by imaging magnetic skyrmions on the surface of Cu₂OSeO₃ with a resolution of only 71 nanometers, and even a helical magnetic phase with a periodicity of only 65 nanometers was clearly resolved.

The newly developed nanoprobes thus open up exciting prospects for the investigation of complex magnetic and quantum physical phenomena and mark a significant advance in high-resolution magnetic field microscopy.

The work is based on a collaboration between researchers from the Department of Physics and the Swiss Nanoscience Institute at the University of Basel, the Physics Institute at the University of Tübingen, the Department of Quantum Electronics at the Physikalisch-Technische Bundesanstalt (Braunschweig), IBM Research Europe (Zurich), and the Institute of Physics at the École Polytechnique Fédérale de Lausanne. 

Further information

Original publication:

Advanced SQUID-on-lever scanning probe for high-sensitivity magnetic microscopy with sub-100-nm spatial resolution
Timur Weber, Daniel Jetter, Jan Ullmann, Simon A. Koch, Simon F. Pfander, Katharina Kress, Andriani Vervelaki , Boris Gross, Oliver Kieler, Ute Drechsler, Priya R. Baral, Arnaud Magrez, Reinhold Kleiner, Armin W. Knoll, Martino Poggio, and Dieter Koelle 
PHYSICAL REVIEW APPLIED 24, 054041 (2025), DOI: 10.1103/6s24-vz3k

Research group Prof. Martino Poggio: 
Poggio Lab