In this European Metrology Project, several National Metrology Institutes, external expert groups and companies team up to develop methods, materials, algorithms and robust calibration methods for quantum-enabled nanoscale magnetic field imaging and measurements based on diamond nitrogen-vacancy (NV) center magnetometry. As one important pilar, magnetic reference material (magnetic multilayers, skyrmion-hosting materials, nanofabricated current-carrying coils, magnetic arrays, and active devices) are developed and validated as transfer standards for comparing nanoscale magnetic measurements across various instrumental platforms and for bridging the new technology with established quantitative magnetic force microscopy (qMFM) methods [1,3].
[1] X. Hu, G. Dai, S. Sievers, A. Fernández-Scarioni, H. Corte-León, R. Puttock, C. Barton, O. Kazakova, M. Ulvr, P. Klapetek, M. Havlíček, D. Nečas, Y. Tang, V. Neu, H.-W. Schumacher, J. Magn. Magn. Mater. 511, 166947 (2020). URL
[2] S. Deussner, D. Suess, C. Abert, F. Bruckner, S. Fähler, P. Heistracher, L. Reichel, V. Neu, Phys. Rev. B 106, 064404 (2022). URL
[3] D.V. Christensen et al., “2024 Roadmap on Magnetic Microscopy Techniques and Their Applications in Materials Science”, J. Phys. Matter. 7, 032501 (2024). URL
Magnetic force microscopy (MFM) is nowadays a powerful standard technique for investigating nanoscale magnetic textures. It relies on a magnetic probe – a tip attached to a cantilever – in a well-defined magnetic state, typically magnetized along the tip axis. Despite its fascinating capabilities, MFM contrast contains artefacts from non-magnetic tip-sample interactions (topography, electrostatic charges, surface potential differences), which can be most effectively subtracted by measuring the sample with two opposite tip magnetization states. To ease this measurement procedure, we develop micrometer-sized coils, with the aim of repeatedly switching the magnetization state of the MFM tips. Being currently structured on flat Si substrates, coils with an inner diameter of 1 µm do allow repeated ms-long, quasistatic current pulses up to 300 mA (see inset of Fig. b), which produce a peak field in the coil center of above 150 mT.
Within a DFG project we team up with our colleagues from the Institute for Solid State Research at IFW-Dresden to optimize coils for appropriate field profiles [1, 2], and analyze the switching behavior of MFM tips by performing series of zero-field MFM measurements, with the tip being exposed to various micro-coil fields. The contrast scaling factor evaluated from these images (Fig. c) allows to construct the tip reversal hysteresis (Fig. b) and confirms that micro-coil fields are sufficiently large to obtain a full contrast inversion on a TbFe-reference sample.
The objective of our project is to foster the small size, the large stray fields (> 150 mT) and the large field gradients (> 0.5 T/µm) of these micro-coils to implement an in-situ differential MFM imaging mode by integrating these micro-coils with the MFM probe.
[1] Patent pending DE 10 2023 135 257.1
[2] A. Sathyadharma Prasad, R. Ravishankar, B. Büchner, V. Neu, T. Mühl, Communications Materials 6, 164 (2025). URL
The functionality of a ferromagnetic device is intimately coupled to the configuration of domains, domain boundaries and the possibility for tailoring them. However, creating complex magnetic textures by design remains very challenging. Here, we developed a simple and versatile strategy to create a wide range of periodic magnetic textures by application of a homogeneous magnetic field and a geometrical transformation of a 2D film into a rolled-up 3D architecture and back. By preparing a magnetic layer system on a polymeric platform including swelling layer, a self-assembled rolling into a multiwinding tubular structure and un-rolling of the functional membrane is obtained. When saturating the rolled-up 3D structure in a simple homogeneous magnetic field, the imprinted configuration translates into a regularly arranged multidomain configuration once the tubular structure is unwound [1]. By tailoring the magnetic anisotropy, a specific angular magnetization configuration is encoded in the 3D state and then finally converted into a spatially periodic magnetic pattern through the geometrical transformation. This combination offers unparalleled possibilities for designing new magnetic or other ferroic micropatterns. In our latest work, a unique cycloidic (spin-spiral) magnetization pattern has been created in a specially designed layer architecture with isotropic exchange-bias properties [2].
[1] V. Neu, I. Soldatov, R. Schäfer, D.D. Karnaushenko, A. Mirhajivarzaneh, D. Karnaushenko, O.G. Schmidt, Creating ferroic micropatterns through geometrical transformation, Nano Letters 21, 9889 (2021). URL
[2] A. Singh, I. Soldatov, R. Schäfer, V. Neu, Designing Stable Periodic Magnetization Textures by Tailoring Anisotropies and Applying Geometrical Transformation, Adv. Func. Mater. 36, 276387 (2026). URL
