Rolled-up architectures for magnetic racetrack memory applications
Final Report Abstract
The goal of this project is to study the effect of curvature of the cylindrical surface on the magnetic domain patterns in thin magnetic films with in-plane and out-of-plane easy axis of magnetization. Two systems are in the focus: (i) magnetic films grown onto curved surfaces of non-magnetic tubes of different length and diameter and (ii) ferromagnetic films rolled-up in a tubular geometry. The key achievements are as follows: (A) Realization of the full-field magnetic soft X-ray tomography: At the beginning of the project, the technique to address the magnetic domain patterns in curved thin films was not available. Therefore, one of the key achievements of the project is the realization of the tomographic approach, which enabled us to carry out such kind of investigations. In brief, we put forth the concept of magnetic soft x-ray tomography and demonstrate its potential by studying hollow tubes with a diameter of several micrometers possessing distinct 3D magnetic patterns. For the very first time, all important details of complex 3D azimuthal and radial magnetized structures are accesses, which are not only fundamentally appealing but are application relevant for medicine and data storage. In particular, azimuthally magnetized hollow tubes are very attractive for application to magnetoimpedance-based sensorics for encephalography devices, due to the enhanced and isotropic sensitivity compared with planar devices. We envision that our development will impact strongly the broad scientific community working in the field of medicine (optimization of the performance of 3D tubular structures for magnetoencephalography), material science community (characterization of 3D-shaped mesoscopic objects with nanometer spatial resolution) and magnetism (study of chiralitydependent domain-wall motion enabling a Cherenkov-like effect for magnons, which is predicted to take place in 3D tubular architectures). (B) Self-assembled on-chip integrated giant magneto-impedance sensorics We put forth a novel method relying on strain engineering to realize arrays of on-chip integrated giant magneto-impedance (GMI) sensors equipped with pick-up coils. The developed technology platform relies on novel photopatternable, thermally and chemically stable imide- and acrylic-based polymers, which allows for microelectronic processing including multiple fabrication steps, e.g. deposition and lithography. A geometrical transformation of an initially planar layout into a tubular 3D architecture stabilizes favorable azimuthal magnetic domain patterns without the need of rapid quenching of the magnetic layer stack in a magnetic field hence boosting the GMI effect 80 times offering remarkable sensitivity of 45 µV/Oe at excitation current of 1 mA at 75 MHz. This work creates a solid foundation for further development of CMOS compatible arrays of gradiometers based on GMI sensorics as needed for magneto-encephalography applications. Development of cost-efficient yet high-performance and even portable magneto-encephalography equipment would bring these unique devices to regular medical institutions offering early stage disease diagnostics with great spatial resolution hence helping to minimize invasivity upon surgical treatment. The results obtained in the frame of this DFG project provided a solid base in the understanding of the curvature- and shape-driven effects in magnetic and non-magnetic architectures. This know-how resulted in new ideas, which allowed to attract futher third party projects.
Publications
- Magnetically capped rolled-up nanomembranes. Nano Letters 12, 3961 (2012)
R. Streubel, D. J. Thurmer, D. Makarov, F. Kronast, T. Kosub, V. Kravchuk, D. D. Sheka, Y. Gaididei, R. Schäfer, and O. G. Schmidt
(See online at https://doi.org/10.1021/nl301147h) - Magnetoresistance of rolled-up Fe3Si nanomembranes. Nanotechnology 23, 255701 (2012)
J. Schumann, K. G. Lisunov, W. Escoffier, B. Raquet, J. M. Broto, E. Arushanov, I. Mönch, D. Makarov, C. Deneke, and O. G. Schmidt
(See online at https://doi.org/10.1088/0957-4484/23/25/255701) - Imaging of buried 3D magnetic rolled-up nanomembranes. Nano Letters 14, 3981 (2014)
R. Streubel, L. Han, F. Kronast, A. A. Unal, O. G. Schmidt, and D. Makarov
(See online at https://doi.org/10.1021/nl501333h) - Spin structures of rolled-up single-layer ferromagnetic nanomembranes. Adv. Mater. 26, 316 (2014)
R. Streubel, J. Lee, D. Makarov, M.-Y. Im, D. Karnaushenko, L. Han, R. Schäfer, P. Fischer, S.-K. Kim, and O. G. Schmidt
(See online at https://doi.org/10.1002/adma.201303003) - Retrieving spin textures on curved magnetic thin films with full-field soft x-ray microscopies. Nature Communications 6, 7612 (2015)
R. Streubel, F. Kronast, P. Fischer, D. Parkinson, O. G. Schmidt, and D. Makarov
(See online at https://doi.org/10.1038/ncomms8612) - Self-assembled on-chip integrated giant magneto-impedance sensorics. Adv. Mater. 27, 6582 (2015)
D. Karnaushenko, D. D. Karnaushenko, D. Makarov, S. Baunack, R. Schäfer, and O. G. Schmidt
(See online at https://doi.org/10.1002/adma.201503127)
