Magnetic field tunable flexible wireless communication device
Experimental Condensed Matter Physics
Synthesis and Properties of Functional Materials
Final Report Abstract
The goal of this project is to study the effect of mechanical strain on magnetotransport properties of magnetic thin films. By combining efforts of two teams (Helmholtz-Zentrum Dresden- Rossendorf and Johannes Gutenberg University of Mainz), we explore fundamental changes in spintronic and spin-orbitronic properties of heterostructures including magnetoresistive thin films with in-plane and out-of-plane easy axis of magnetization under applied strain. To understand the fundamentals of the underlying physical effects, we have performed a detailed study of the spin-orbit torques (field-like and damping-like torques) in magnetic heterostructures prepared on piezoactuators. Among other findings, key results include the demonstration that the magnitude of current-induced spin-orbit torques in thin perpendicularly magnetized CoFeB films can be tuned and even increased significantly by electric-field generated piezoelectric strain. Using theoretical calculations, we uncover that the subtle interplay of spin-orbit coupling, crystal symmetry, and orbital polarization is at the core of the observed strain dependence of spin-orbit torques. The strain dependent effects are very sensitive to the layer stack as for instance in a Ta/CoFeB/Ta/MgO stack, the damping-like torque is very small and strain results in a substantial change of the field-like torque. We explain the observed behavior by a combined action of the current-induced reduction of the magnetic anisotropy assisted or counteracted by the generated strain of different symmetry. On the fundamental physics side, we have dedicated much attention to the study of the impact of geometrical curvature on the magnetization reversal in curved magnetic stripes and thin films. One of the key achievements is the experimental confirmation that the effects of the geometrical curvature results in the pinning of magnetic domain walls at local bends. The physical origin of this pinning is determined to be related to the curvature-induced Dzyaloshinskiy-Moria interaction (DMI). This is the first experimental validation of the cornerstone prediction of the theory of curvilinear magnetism - namely, the emergence of the curvature-induced chiral interaction stemming from the exchange interaction. These fundamental understanding of the effects of strain and geometrical curvature on the magnetotransport performance and switching behaviour of magnetic thin films is crucial for the optimisation of mechanically flexible and stretchable magnetic field sensors. The discovered additional pinning mechanism of magnetic domain walls on bends and twists of a geometrically curved magnetic stripes has a severe impact on the realisation and optimisation of magnetic field sensors. Indeed, any pinning results in an enchancement of the coercive field, which might affect the sensitivity of the magnetic field sensors especially in a low field range. Hence, making use of the know-how of the strain impact on the magnetic properties, we have then put much efforts on the realisation of flexible magnetic field sensors (spin valve sensors and anisotropic magnetoresistance sensors) and the investigation of their mechanical stability to static and dynamic bending tests. These activities resulted in the realisation of the very first mechanically flexible electronic compass (device can be operated in a geomagnetic field), which was successfully used as a novel human-machine interface for virtual reality applications. Furthermore, we developed the very first tunable magnetoreceptive platform for on-skin touchless interactive electronics based on flexible spin valve sensor elements with dedicated out- of-plane sensitivity to magnetic fields. Depending on the material properties of the on-skin switch used, the virtual functions can be impervious to or controlled by ambient magnetic stimuli. We envision that this technology platform will pave the way towards magnetoreceptive human- machine interfaces or virtual- and augmented reality applications, which are intuitive to use, energy efficient, and insensitive to external magnetic disturbances. The results obtained in the frame of this DFG project provided a solid base in the understanding of the strain and curvature effects in low-dimensional magnetic architectures. This know-how resulted in new ideas, which allowed to attract follow-up third party funding to continue this research including projects financed via the Federal Ministry of Education and Research (BMBF), Federal Ministry for Economic Affairs and Energy (BMWi), the German Research Foundation (DFG) and the EU.
Publications
- Electronic-skin compasses for geomagnetic field-driven artificial magnetoreception and interactive electronics. Nature Electronics 1, 589 (2018)
G. S. Cañón Bermúdez, H. Fuchs, L. Bischoff, J. Fassbender, D. Makarov
(See online at https://doi.org/10.1038/s41928-018-0161-6) - Experimental Observation of Exchange-Driven Chiral Effects in Curvilinear Magnetism. Phys. Rev. Lett. 123, 077201 (2019)
O. M. Volkov, A. Kákay, F. Kronast, I. Mönch, M.-A. Mawass, J. Fassbender, D. Makarov
(See online at https://doi.org/10.1103/PhysRevLett.123.077201) - Piezo-electrical control of gyration dynamics of magnetic vortices. Appl. Phys. Lett. 115, 062404 (2019)
M. Filianina, L. Baldrati, T. Hajiri, K. Litzius, M. Foerster, L. Aballe, M. Kläui
(See online at https://doi.org/10.1063/1.5110169) - Electric-Field Control of Spin-Orbit Torques in Perpendicularly Magnetized W/CoFeB/MgO Films. Phys. Rev. Lett. 124, 217701 (2020)
M. Filianina, JP. Hanke, K. Lee, D.S. Han, S. Jaiswal, A. Rajan, G. Jakob, Y. Mokrousov, M. Kläui
(See online at https://doi.org/10.1103/PhysRevLett.124.217701) - Flexible Magnetoreceptor with Tunable Intrinsic Logic for On-Skin Touchless Human-Machine Interfaces. Vladymyrskyi, J. Fassbender, M. Albrecht, G. Varvaro, D. Makarov Adv. Funct. Mater. 31, 2101089 (2021)
P. Makushko, E. S. Oliveros Mata, G. S. Cañón Bermúdez, M. Hassan, S. Laureti, C. Rinaldi, F. Fagiani, G. Barucca, N. Schmidt, Y. Zabila, T. Kosub, R. Illing, O. Volkov, I. Vladymyrskyi, J. Fassbender, M. Albrecht, G. Varvaro, D. Makarov
(See online at https://doi.org/10.1002/adfm.202101089) - Impact of the interplay of piezoelectric strain and current-induced heating on the field-like spin-orbit torque in perpendicularly magnetized Ta/Co20Fe60B20/Ta/MgO film. Appl. Phys. Lett. 118, 032401 (2021)
M. Filianina, Z. Wang, L. Baldrati, K. Lee, M. Vafaee, G. Jakob, M. Kläui
(See online at https://doi.org/10.1063/5.0035869)
