Mixed ferromagnetic/antiferromagnetic hybrid phase in stripe and bubble domain structures for magnonic crystal and race track applications

• Applicant: Professor Dr. Olav Hellwig
• Subject Area: Experimental Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 514946929

In this project we want to study a new perpendicular magnetic anisotropy (PMA) hybrid structure consisting of periodic ferromagnetic (FM) out-of-plane (oop) up and down stripe or bubble domains separated by antiferromagnetic (AFM) in-plane (ip) Bloch-type or mixed Bloch-Neel-type domain walls. We are using a double multilayer magnetic thin film platform [1] to control precisely the various involved magnetic energy contributions in order to stabilize this new mixed FM/AFM hybrid phase. Targeting an energy balance characterized by strong PMA with simultaneously large demagnetization fields, thus promoting highly periodic stripe domain patterns [1-3], we add to this energy setting a comparably weak AFM interlayer exchange coupling (IEC). For this so far unexplored magnetic energy constellation we expect that the weak AFM-IEC only reveals itself within the ip domain walls, as inside the oop stripe domains itself the AFM-IEC is overcome by the strong demagnetization fields perpendicular to the film plane. After investigating the exact structure of this new phase by experimental techniques (magnetometry, magnetic force microscopy and Lorentz transmission electron microscopy) as well as micromagnetic simulations, we will perform a detailed study of the static properties and field reversal behavior of this new FM/AFM hybrid phase. As part of this investigation, we will also determine the stability region of the phase within the complex energy landscape consisting of PMA, demagnetization and AFM-IEC energy at remanence as well as in combination with externally applied magnetic fields. In particular, we will explore the stabilization of highly-periodic parallel stripe and quasi-hexagonal bubble domain patterns at remanence by previously exposing the system to specific magnetic field protocols [3]. Finally, we want to focus on two possible applications for this new FM/AFM hybrid structure: 1) magnetic race track memory type systems based on magnetic bubble propagation via electric current pulses along a lithographically or otherwise confined magnetic strip line [4,5] using Hall effect analysis and magnetic force microscopy 2) fabrication and optimization of reprogrammable self-organized magnonic crystal structures based on highly-periodic parallel stripe domain patterns [6,7]. [1] O. Hellwig et al., J. Mag. Mag. Mat. 319, 13 (2007). [2] O. Hellwig et al., Physica B: Condensed Matter 336, 136 (2003). [3] L. Fallarino et al., Phys. Rev. B 99, 024431 (2019). [4] S. S. P. Parkin et al., Science 320, 190 (2008). [5] R. Tomasello et al., Scientific Reports 4, 6784 (2014). [6] C. Banerjee et al., Phys. Rev. B 96, 024421 (2017). [7] P. Gruszecki et al., Book chapter in “SSP-70 - RECENT ADVANCES IN TOPOLOGICAL FERROICS AND THEIR DYNAMICS and in Solid State Physics, Volume 70 (2019).

• DFG Programme: Research Grants
• International Connection: India, Poland
• Cooperation Partners: Professor Dr. Anjan Barman; Professor Dr. Maciej Krawczyk