Abstract
Unusual features in the Hall Resistivity of thin film systems are frequently associated with whirling spin textures such as Skyrmions. A host of recent investigations of Hall Hysteresis loops in SrRuO3 heterostructures have provided conflicting evidence for different causes for such features. We have constructed an SrRuO3-PbTiO3 (Ferromagnetic – Ferroelectric) bilayer that exhibits features in the Hall Hysteresis previously attributed to a Topological Hall Effect, and Skyrmions. Here we show field dependent Magnetic Force Microscopy measurements throughout the key fields where the ‘THE’ presents, revealing the emergence to two periodic, chiral spin textures. The zero-field cycloidal phase, which then transforms into a ‘double-q’ incommensurate spin crystal appears over the appearance of the ‘Topological-like’ Hall effect region, and develop into a ferromagnetic switching regime as the sample reaches saturation, and the ‘Topological-like’ response diminishes. Scanning Tunnelling Electron Microscopy and Density Functional Theory is used to observe and analyse surface inversion symmetry breaking and confirm the role of an interfacial Dzyaloshinskii–Moriya interaction at the heart of the system.
Highlights
Unusual features in the Hall Resistivity of thin film systems are frequently associated with whirling spin textures such as Skyrmions
We have investigated the magnetic domain evolution in ferroelectric-SRO system, where dielectric polarisation is expected to induce a strong symmetry breaking, identifying a chiral spin crystal that emerges over the topological Hall effect (THE) magnetic field range
We show theoretically and with atomic-resolution scanning transmission electron microscopy (STEM) that the system exhibits broken surface inversion symmetry, itself causing a large interfacial DMI (iDMI)
Summary
The emergence of a topological Hall effect (THE)[1,2] in SrRuO3 (SRO) revealed by unusual peaks in Hall resistivity has been attributed to presence of a skyrmion phase Such skyrmion signature features have been previously reported in SRO thin films when combined with a spin-orbit coupling layer SrIrO33,4 and ferroelectric systems[5,6]. The interfacial DMI (iDMI) was shown to be at the heart of thin film systems that exhibited a THE-like response[3,6,7,8] Such an interaction relies on broken surface inversion symmetry, which is expected when combining metallic perovskite magnetic materials with a ferroelectric[5,6,21], giving rise to Rashba spin-orbit coupling[22], which in turn acts as the dominant contributing factor to the iDMI. We demonstrate that ferroelectric polarisation induces such a magnetic chiral phase in a ferromagnet–ferroelectric bilayer system
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