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Quantum-calibrated magnetic force microscopy

More reliable magnetic field measurements in the nanometer range

PTBnews 1.2022
Especially interesting for

magnetic sensor technology

magnetic metrology

A classical measurement system for measuring magnetic field distributions, which vary spatially on the nanometer scale, was calibrated by means of an atomic quantum sensor for the first time. This new calibration procedure does not depend on simplifying model assumptions and allows more reliable measurements of magnetic field distributions with high spatial resolution.

Schematic representation of the measurement setup used for calibrating an MFM tip by means of a quantum sensor. The MFM tip (turquoise) generates a magnetic stray field which can be measured precisely over a single NV center (yellow) in a diamond substrate (blue). If the tip is scanned over the NV center, its stray field distribution is obtained – and thus quantum-accuracy information on its magnetic imaging properties is also gained.

To develop future magnetic components such as sensors and data storage devices, industry needs traceable magnetic field measuring systems with the best possible spatial resolution. The most widespread method for measuring magnetic field distributions on the nanometer scale is magnetic force microscopy (MFM). In MFM, a magnetic tip is moved a few nanometers above a sample surface while measuring the force which acts on the tip in the magnetic field of the sample. To be able to calculate the magnetic field strength from this force in SI units, the magnetic properties of the tip must be known very accurately. For this purpose, simplifying models combined with measurements on magnetic reference samples have been used to date.

Within the scope of a cooperation project between PTB and the University of Ulm, the magnetic properties of such a magnetic tip have now been characterized precisely for the first time by means of a quantum sensor. This nitrogen vacancy (NV) center sensor consists of a single atomic lattice defect in a diamond crystal whose optical spectrum depends on the external magnetic field. In the experiments performed, the magnetic tip was scanned in a plane over the NV center, and the optical spectrum was measured at each point. Based on these measurements, a map of the magnetic field emanating from the tip was derived. The tip’s magnetic properties that are relevant to magnetic force microscopy were then determined from this map. After this procedure, the tip was quantum calibrated and could be used for precise and reliable magnetic field measurements on the nanoscale.

In further investigations, it is also planned to set up such a measuring system to characterize MFM tips at PTB. In this way, it would be possible to perform MFM measurements using quantum-calibrated tips directly at PTB in the future.


Hans Werner Schumacher
Department 2.5
Semiconductor Physics and Magnetism
Phone: +49 531 592-2500
Opens local program for sending emailhans.w.schumacher(at)ptb.de

Scientific publication

B. Sakar, Y. Liu, S. Sievers, V. Neu, J. Lang, C. Osterkamp, M. L. Markham, O. Öztürk, F. Jelezko, H. W. Schumacher: Quantum calibrated magnetic force microscopy. Phys. Rev. B, 104, 214427 (2021)