Seminars
Oleksandr Pylypovskyi (HZDR): Magnetic textures in bulk and thin film Cr2O3
Hybrid, VBL 204 & Zoom
The spin degree of freedom in magnetically ordered materials is an important aspect for a variety of research directions. Antiferromagnets represent a broad class of systems with compensated or almost compensated net magnetization. On one side, it is a factor in the complications of their experimental investigation. However, on the other side, they offer unique features on ultrafast dynamics, strong robustness regarding external magnetic fields and delicate symmetry-driven phenomena in spin torques and multiferroicity. Specific research attention is paid to the properties of antiferromagnetic solitons as potential information carriers and the surface properties at which the readout of the magnetic state is performed. Here, we focus on the seminal magnetoelectric antiferromagnet Cr2O3 (chromia) with the easy-axis magnetic anisotropy.
In bulk single crystal chromia, the multidomain state is not favorable due to thermodynamic reasons, thus the stabilization of domain walls is possible on the defects. In particular, the litographically partterned surface topography of the sample can serve as the pinning landscape for the domain wall. The spatial inhomogeneity of this landscape allows to uncover the mechanical properties of the magnetic textures such as elastic deformation of the domain wall plane governed by the exchange boundary conditions [1]. Extension of this model onto chiral antiferromagnets with an inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) shows that the domain walls and skyrmions possess a substantial modification of their shape approaching surface and side faces of the sample. These modifications limit the minimal size of racetracks to keep the bulk-like properties of magnetic solitons [2].
The surface of an antiferromagnet itself can substantially change its magnetic state. Chromia possesses two nominally compensated high-symmetry planes with an experimental evidence of a finite magnetization. The latter can be understood in terms of the surface magnetic symmetry group which supports a homogeneous DMI and can even change the bulk collinear antiferromagnetic ordering to a canted ferrimagnetic one [3].
In contrast to bulk, the chromia thin films are commonly in the multidomain state, which is determined by their granular structure. The domain wall pinning at the defects depends on the defect properties. Therefore, the visual analysis of the domain picture obtained, e.g., via Nitrogen vacancy magnetometry can be used as a source of quantification of the inter-grain coupling in the thin film [4] and, even quantification of such exotic phenomena like thermally driven flexomagnetism [5].
[1] N. Hedrich, K. Wagner, O. V. Pylypovskyi et al., Nat. Phys., 17, 574 (2021)
[2] O. V. Pylypovskyi, A. V. Tomilo, D. D. Sheka et al., Phys. Rev. B 103, 134413 (2021)
[3] O. V. Pylypovskyi, S. F. Weber, P. Makushko et al., Phys. Rev. Lett. 132, 226702 (2024)
[4] O. V. Pylypovskyi, N. Hedrich, A. V. Tomilo et al., Phys. Rev. Applied, 20, 014020 (2023)
[5] P. Makushko, T. Kosub, O. V. Pylypovskyi et al. Nat. Comm., 13, 6745 (2022)
In bulk single crystal chromia, the multidomain state is not favorable due to thermodynamic reasons, thus the stabilization of domain walls is possible on the defects. In particular, the litographically partterned surface topography of the sample can serve as the pinning landscape for the domain wall. The spatial inhomogeneity of this landscape allows to uncover the mechanical properties of the magnetic textures such as elastic deformation of the domain wall plane governed by the exchange boundary conditions [1]. Extension of this model onto chiral antiferromagnets with an inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) shows that the domain walls and skyrmions possess a substantial modification of their shape approaching surface and side faces of the sample. These modifications limit the minimal size of racetracks to keep the bulk-like properties of magnetic solitons [2].
The surface of an antiferromagnet itself can substantially change its magnetic state. Chromia possesses two nominally compensated high-symmetry planes with an experimental evidence of a finite magnetization. The latter can be understood in terms of the surface magnetic symmetry group which supports a homogeneous DMI and can even change the bulk collinear antiferromagnetic ordering to a canted ferrimagnetic one [3].
In contrast to bulk, the chromia thin films are commonly in the multidomain state, which is determined by their granular structure. The domain wall pinning at the defects depends on the defect properties. Therefore, the visual analysis of the domain picture obtained, e.g., via Nitrogen vacancy magnetometry can be used as a source of quantification of the inter-grain coupling in the thin film [4] and, even quantification of such exotic phenomena like thermally driven flexomagnetism [5].
[1] N. Hedrich, K. Wagner, O. V. Pylypovskyi et al., Nat. Phys., 17, 574 (2021)
[2] O. V. Pylypovskyi, A. V. Tomilo, D. D. Sheka et al., Phys. Rev. B 103, 134413 (2021)
[3] O. V. Pylypovskyi, S. F. Weber, P. Makushko et al., Phys. Rev. Lett. 132, 226702 (2024)
[4] O. V. Pylypovskyi, N. Hedrich, A. V. Tomilo et al., Phys. Rev. Applied, 20, 014020 (2023)
[5] P. Makushko, T. Kosub, O. V. Pylypovskyi et al. Nat. Comm., 13, 6745 (2022)