31.01.2022
A classical measurement system for measuring magnetic field distributions, spatially varying on the nanometer scale, was, for the first time, calibrated by means of an atomic quantum sensor. The new calibration procedure does not depend on simplifying model assumptions and allows more reliable measurements of magnetic field distributions with high spatial resolution.
To develop future magnetic components such as sensors and data memories, 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 the sample surface and the force is measured which acts on the tip in the magnetic field of the sample. To be able to calculate the magnetic field strength in SI units from this force, 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 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 from which the tip’s magnetic properties that are relevant to magnetic force microscopy were determined. 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 is possible to perform MFM measurements using quantum-calibrated tips directly at PTB.
Figure: 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, one obtains its stray field distribution – and thus quantum-accuracy information on its magnetic imaging properties.
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, accepted for publication.
Department 2.5 “Semiconductor Physics and Magnetism”