Magnetic exchange coupled heterostructures on spherical nanoparticles
Final Report Abstract
This project is dedicated to the investigation of the magnetic coupling phenomena in heterostructures consisting of magnetically hard and soft sub-systems. The main emphasis is on fabrication of those hard-soft composites on arrays of non-magnetic spherical particles acting as convenient and easily accessible curvature templates for preparation of magnetic confined nano- and micro-structures. The fundamentals of the coupling phenomena in hardsoft composites as well as the prospective application directions are highlighted. The key achievements are as follows: (A) Magnetic and structural properties of the FePtCu/[Co/Pt] exchange coupled composites: We gained deep insight into the structural origin of the reduced magnetic coupling at the interface between hard magnetic FePtCu ternary alloy and softer Co/Pt multilayer stacks. By performing extended electron microscopy and spectroscopy investigations, we pinpoint the natural Fe-O at the top surface of FePtCu alloy to be responsible for mediating the coupling in the composite. We successfully solved this issue and demonstrate that the interlayer crystallization as well as Cu diffusion are the two efficient sources allowing to enhance the exchange coupling between hard and soft sub-systems. Furthermore, we were able to experimentally prove the theoretical prediction that the pinning field can be reduced by reducing the difference between the magnetic anisotropy constants of the two layers. This result shows that control of the magnetic properties of the soft and hard layers is vital for the performance of the exchange coupled composites for magnetic data storage applications. Additional temperature treatment of the bilayer stack has offered a further reduction of the pinning field due to a structural phase transition of the iron oxide present at the interface between the hard and soft layers. (B) Imprinting non-collinear spin textures in exchange coupled composites: Recently, we have successfully demonstrated an alternative route to design magnetic heterostructures where specific spin textures resembling vortices or skyrmions with distinct topological charges can be tailored at ambient temperatures. This was achieved by vertically stacking two magnetic nanopatterns with in-plane, e.g. Permalloy, and out-of-plane, e.g. Co/Pd multilayers, magnetization and imprinting the in-plane non-collinear spin textures into the out-of-plane magnetized material. Tuning the interlayer coupling strength, a gradual transition in the magnetic pattern of the out-of-plane layer via skyrmionic state towards a vortex spin texture was observed allowing to control the spin textures deliberately. We successfully imaged these states in magnetic cap structures consisting of [Co/Pd]/Pd/Py stacks using transmission soft x-ray microscopy. Furthermore, we predicted theoretically and verified experimentally that imprinted magnetic states with distinct topological properties can be reversibly switched by exposing the structure to a small magnetic field. The experimentally observed stabilization of and digital switching between topologically nonequivalent states is an essential step towards the realization of data storage based on topological properties of magnetic nanostructures. 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 several national and EU-funded third party projects.
Publications
- Catalytic Janus motors on microfluidic chip: deterministic motion for targeted cargo delivery. ACS Nano 6, 3383 (2012)
L. Baraban, D. Makarov, R. Streubel, I. Mönch, D. Grimm, S. Sanchez, and O. G. Schmidt
(See online at https://doi.org/10.1021/nn300413p) - Equilibrium magnetic states in individual hemispherical Permalloy caps. Appl. Phys. Lett. 101, 132419 (2012)
R. Streubel, V. P. Kravchuk, D. D. Sheka, D. Makarov, F. Kronast, O. G. Schmidt, and Y. Gaididei
(See online at https://doi.org/10.1063/1.4756708) - 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) - Fuel-free locomotion of Janus motors: Magnetically induced thermophoresis. ACS Nano 7, 1360 (2013)
L. Baraban, R. Streubel, D. Makarov, L. Han, D. D. Karnaushenko, O. G. Schmidt, and G. Cuniberti
(See online at https://doi.org/10.1021/nn305726m) - EXAFS investigation of the role of Cu on the chemical order and lattice distortion in L10 FePtCu thin films. J. Appl. Cryst. 47, 1722 (2014)
S. Laureti, C. Brombacher, D. Makarov, M. Albrecht, D. Peddis, G. Varvaro, and F. D’Acapito
(See online at https://doi.org/10.1107/S1600576714019268) - Scaling dependence and tailoring of the pinning field in FePt based exchange coupled composite media. Nanotechnology 25, 045604 (2014)
J. Lee, D. Makarov, C. Brombacher, B. Dymerska, D. Suess, M. Albrecht, and J. Fidler
(See online at https://doi.org/10.1088/0957-4484/25/4/045604) - Manipulating topological states by imprinting non-collinear spin textures. Scientific Reports 5, 8787 (2015)
R. Streubel, L. Han, M.-Y. Im, F. Kronast, U. K. Rößler, F. Radu, R. Abrudan, G. Lin, O. G. Schmidt, P. Fischer, and D. Makarov
(See online at https://doi.org/10.1038/srep08787) - Structural and magnetic properties of Cu-alloyed FePd films. J. Magn. Magn. Mater. 381, 316 (2015)
A. Polit, D. Makarov, C. Brombacher, M. Krupinski, M. Perzanowski, Y. Zabila, M. Albrecht, M. Marszałek
(See online at https://doi.org/10.1016/j.jmmm.2015.01.017)
