Topological Spin Textures in Magnetic Multilayers

Topological spin textures, such as vortices or skyrmions, are attracting significant attention because of their intriguing fundamental properties as well as their promising applicability in memory devices or spin torque oscillators. A particular topological texture that was theoretically predicted is the two-dimensional hedgehog state, also known as ’spin meron’. It had been unclear, however, whether this kind of highly divergent magnetization structure may occur in real systems. Only recently, evidence for the existence of meron-like pair states was reported for the case of trilayer elements consisting of two ferromagnetic layers and a non-ferromagnetic interlayer [1]. On this background, a direct proof for the existence of meron-like states in trilayer elements via direct magnetic imaging will be presented. It will also be shown that in the presence of biquadratic interlayer exchange coupling, such meron-like pair states may even represent the magnetic ground state of the system. Interestingly, the highly divergent magnetization distribution induces an additional, three-dimensional torus vortex that in-turn causes a symmetry break for the possible topological pair configurations [2]. In addition the dynamic properties of vertically coupled topological spin textures will be addressed, where the focus will be set on spin wave emission processes in such systems.
References: [1] C. Phatak et al., Phys. Rev. Lett. 108, 067205 (2012). [2] S. Wintz et al., Phys. Rev. Lett. 110, 177201 (2013).