START Fellow 2021

Technical University of Munich

TUM School of Natural Sciences

James-Franck-Str. 1

85748 Garching

Tel. +49 89 289 12660


Research website

Research is a systematic way to convert your imagination into concepts with images of structures, setups, and processes.


Information exchange with high cooperativity achieved by strong magnon-photon coupling is essential for quantum information applications. This strong coupling can be achieved by inserting a magnet with ultra-low damping into a high quality microwave cavity. However, the choice of available magnetic materials for this purpose is very limited and investigation of new quantum materials is strongly limited by inability to grow sufficiently large, high-purity and single-phase crystals.

The current project aims to investigate and design new insulating magnets suitable for quantum hybrid systems. The major task is to establish appropriate methods to grow these materials with desired purity and optimized magnetic damping.

Research focus: My main research focus lies within the chiral magnetic insulators such as Cu2OSeO3. It has very low magnetic damping and offer a strong coupling to microwave photons along with a very rich magnetic phase diagram. It hosts several magnetic textures including spin helices and skyrmions, which are nanometer sized twists in magnetization. I search for new ways to grow these systems in a controlled fashion and magnetically characterize them.



Task-adaptive physical reservoir computing

Lee, O., Wei, T., Stenning, K. D., Gartside, J. C., Prestwood, D., Seki, S., Aqeel, A., Karube, K., Kanazawa, N., Taguchi, Y., Back, C., Tokura, Y., Branford, W. R., & Kurebayashi, H.

Nature materials 23(1), 79–87 (2023).

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Reservoir computing is a neuromorphic architecture that may offer viable solutions to the growing energy costs of machine learning. In software-based machine learning, computing performance can be readily reconfigured to suit different computational tasks by tuning hyperparameters. This critical functionality is missing in ‘physical’ reservoir computing schemes that exploit nonlinear and history-dependent responses of physical systems for data processing. Here we overcome this issue with a ‘task-adaptive’ approach to physical reservoir computing. By leveraging a thermodynamical phase space to reconfigure key reservoir properties, we optimize computational performance across a diverse task set. We use the spin-wave spectra of the chiral magnet Cu2OSeO3 that hosts skyrmion, conical and helical magnetic phases, providing on-demand access to different computational reservoir responses. The task-adaptive approach is applicable to a wide variety of physical systems, which we show in other chiral magnets via above (and near) room-temperature demonstrations in Co8.5Zn8.5Mn3 (and FeGe).

DOI: 10.1038/s41563-023-01698-8

Resonant Elastic X-Ray Scattering of Antiferromagnetic Superstructures in EuPtSi3

Simeth, W., Bauer, A., Franz, C., Aqeel, A., Bereciartua, P. J., Sears, J. A., Francoual, S., Back, C. H., & Pfleiderer, C.

Phys. Rev. Lett. 130(26), 266701 American Physical Society, (2023).

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We report resonant elastic x-ray scattering of long-range magnetic order in EuPtSi3, combining different scattering geometries with full linear polarization analysis to unambiguously identify magnetic scattering contributions. At low temperatures, EuPtSi3 stabilizes type A antiferromagnetism featuring various long-wavelength modulations. For magnetic fields applied in the hard magnetic basal plane, well-defined regimes of cycloidal, conical, and fanlike superstructures may be distinguished that encompass a pocket of commensurate type A order without superstructure. For magnetic field applied along the easy axis, the phase diagram comprises the cycloidal and conical superstructures only. Highlighting the power of polarized resonant elastic x-ray scattering, our results reveal a combination of magnetic phases that suggest a highly unusual competition between antiferromagnetic exchange interactions with Dzyaloshinsky-Moriya spin-orbit coupling of similar strength.

DOI: 10.1103/PhysRevLett.130.266701

Hybrid magnetization dynamics in Cu2OSeO3/NiFe heterostructures

Lüthi, C., Flacke, L., Aqeel, A., Kamra, A., Gross, R., Back, C. & Weiler, M.

Appl. Phys. Lett. 122(1), 012401 (2023).

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We investigate the coupled magnetization dynamics in heterostructures of a single crystal of the chiral magnet Cu2OSeO3 (CSO) and a polycrystalline ferromagnet NiFe (Py) thin film using broadband ferromagnetic resonance (FMR) at cryogenic temperatures. We observe the excitation of a hybrid mode (HM) below the helimagnetic transition temperature of CSO. This HM is attributed to the spin dynamics at the CSO/Py interface. We study the HM by measuring its resonance frequencies for in plane rotations of the external magnetic field. We find that the HM exhibits dominantly fourfold anisotropy in contrast to the FMR of CSO and Py.

DOI: 10.1063/5.0128733

Chiral surface spin textures in Cu2OSeO3 unveiled by soft X-ray scattering in specular reflection geometry

Ukleev, V., Luo, C., Abrudan, R., Aqeel, A., Back, C. H. & Radu, F.

Science and Technology of Advanced Materials 23(1), 682-690 (2022).

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Resonant elastic soft X-ray magnetic scattering (XRMS) is a powerful tool to explore long-periodic spin textures in single crystals. However, due to the limited momentum transfer range imposed by long wavelengths of photons in the soft x-ray region, Bragg diffraction is restricted to crystals with the large lattice parameters. Alternatively, small-angle X-ray scattering has been involved in the soft energy X-ray range which, however, brings in difficulties with the sample preparation that involves focused ion beam milling to thin down the crystal to below a few hundred nm thickness. We show how to circumvent these restrictions using XRMS in specular reflection from a sub-nanometer smooth crystal surface. The method allows observing diffraction peaks from the helical and conical spin modulations at the surface of a Cu2OSeO3 single crystal and probing their corresponding chirality as contributions to the dichroic scattered intensity. The results suggest a promising way to carry out XRMS studies on a plethora of noncentrosymmetric systems hitherto unexplored with soft X-rays due to the absence of the commensurate Bragg peaks in the available momentum transfer range.


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