In the group of Volker Neu we are interested in resolving the details of magnetic microstructures and complex magnetic textures on the nanoscale, mainly by advanced quantitative magnetic force microscopy techniques.
A current focus lies on field or current driven domain wall motion in possible memory or sensor devices and on exploring self-assembled roll-up technology for tailoring anisotropies and domain configurations.
B. Singh, J. A. Otálora, T. Kang, I. Soldatov, D.D. Karnaushenko, C. Becker, R. Schäfer, D. Karnaushenko, V. Neu, O.G. Schmidt,
Self-assembly as a tool to study microscale curvature and strain-dependent magnetic properties
npj Flex. Electron. 6, 76 (2022).
Tuning anisotropy with strain and curvature has become a promising ingredient in modern electronics, such as in flexible and stretchable magnetoelectronic devices. By applying a self-assembly rolling technique using a polymeric platform developed by our colleagues from TU Chemnitz, we provide a template that allows homogeneous and controlled bending of a functional layer adhered to it, irrespective of its shape and size. This is an intriguing possibility to tailor the sign and magnitude of the surface strain of integrated, micronsized devices. In our current work we induce an azimuthal anisotropy by rolling-down permalloy structures with positive magnetostriction as visible in the Kerr micrographs, and quantify the induced anisotropy by means of an integrated AMR sensor. By controlling the rolling orientation and diameter (not shown here), sign and magnitude of strain and thus anisotropy can be tuned.
The functionality of a ferroic device is intimately coupled to the configuration of domains, domain boundaries and the possibility for tailoring them. We developed a novel approach which allows the creation of new, metastable magnetic multidomain patterns with tailored wall configurations through a self-assembled geometrical transformation. By preparing a magnetic layer system on a polymeric platform including swelling layer, a repeated self-assembled rolling into a multiwinding tubular structure and un-rolling of the functional membrane is obtained. When polarizing 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 un-wound. The process is linked to the employed magnetic anisotropy with respect to the surface normal, and the geometrical transformation connects the angular with the lateral degrees of freedom. This combination offers unparalleled possibilities for designing new magnetic or other ferroic micropatterns.
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).
AC-excited domain wall processes are the heart of modern domain wall (DW) based microscale devices such as giant-magneto impedance sensors and magnetophoretic circuit. However, it remains a major challenge for magnetic microscopies to follow the DW trajectory and amplitude while it is in motion.
Here we report an imaging approach to investigate DW dynamics with nanoscale spatial resolution employing conventional magnetic force microscopy (MFM) -- a powerful technique that is, however, largely unexplored concerning imaging of time-dependent domain processes. The method is based on a quantitative assessment of the time- averaged MFM phase shift signal and its description by the locally varying dwell time function of an oscillating DW. With this technique, we quantify the oscillations of a 180° Nèel domain wall in a patterned permalloy rectangle as a function of external magnetic field strength, frequency, magnetic structure size, thickness, and strain-induced anisotropy – down to a resolution of 60 nm.
Being capable to operate at large frequencies, this new method opens the path for an in-depth study of a variety of fundamental and technologically relevant materials properties, such as local magnetic susceptibilities, wall mobilities, and domain wall masses.
B. Singh, R. Ravishankar, J.A. Otálora, I. Soldatov, R. Schäfer, D. Karnaushenko, V. Neu, O.G. Schmidt,
Direct imaging of field-driven nanoscale domain wall oscillations in Landau structures
Nanoscale DOI: 10.1039/d2nr03351h (2022).
Magnetic force microscopy (MFM) has established its place as an extremely valuable method for the investigation of magnetic microstructures on the nanometer scale. Beyond being a purely qualitative imaging technique, quantitative MFM (qMFM) offers access to 3-dimensional magnetic textures on the nanometer scale in the surface-near region of arbitrary samples, when the imaging properties of the tip are quantitatively characterized. The Magnetic Microscopy and Thin Film Device group at IFW has long year experience, working on all relevant aspects of qMFM: tip calibration routines, dedicated calibration samples, probe development, and application to the study of various magnetic microtextures.
The latest development directly quantifies the 2D tip stray field function via single nitrogen vacancy (NV) magnetometry. This constitutes the first quantum calibrated measurement of an MFM probe’s TTF and hence opens the path to quantum traceable nanoscale stray magnetic field measurements.
H. Corte-León, V. Neu, A. Manzin, C. Barton, Y. Tang, M. Gerken, P. Klapetek, H.-W. Schumacher and O. Kazakova
Comparison and validation of different magnetic force microscopy calibration schemes
Small 16, 1906144 (2020).
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).
last updated: 2022-09-26 hs