Magnetische Austauschkopplung und elektrisches Schalten in multiferroischen BiFeO3/Doppelperowskit Heterostrukturen
Herstellung und Eigenschaften von Funktionsmaterialien
Zusammenfassung der Projektergebnisse
The final goal of the project was to implement and understand switching of the magnetization using an electric voltage in a double perovskite and to investigate interface effects at a multiferroic/ferromagnet interface using new material systems. We wanted to achieve this using multiferroic materials, especially BiFeO3 (BFO), that not only possess a ferroelectric but also a (anti-)ferromagnetic order parameter at room temperature and couple this electric order parameter to ferrimagnets, in thin film heterostructures. For a reduced roughness we substitute a fraction of Bi with Ba in the BFO layer and perform these experiments with barium doped BFO (BBFO). However, in the course of the project it turned out that the growth conditions for a well ordered double perovskite are incompatible with that of the ferroelectric layer. The bilayers show poor quality due to the decomposition of one layer at the deposition conditions of the consecutive layer. While the BBFO layer decomposes due to the high deposition temperature of the Sr2FeMoO6 (SFMO), the SFMO oxidizes during the deposition of the BBFO layer. We conclude that the high quality heterostructure out of these materials cannot be grown using our methods. From our understanding, this holds also for other BBFO/double perovskite material combinations. The results of this growth study were published. For an alternative approach, we therefore investigated a replacement for BFO. A different multiferroic, TmFeO3, was tested that is ferroelectric in a hexagonal phase but antiferromagnetic in its cubic modification. We could grow it in both type of modifications depending on the chosen substrate. For application as a ferroelectric we intended to grow it on Pt(111) layers following literature. However, at the elevated temperatures needed for epitaxial growth always a dewetting of the Pt layer occurred, prohibiting the ferroelectric investigations planned. At the same time we realized that the spin interactions of the cubic antiferromagnetic compound with the Pt overlayer could be exploited to test the spin state of the antiferromagnet. Using spin dependent magnetoresistance measurements we could demonstrate the spin reorientation transition in thin films of TmFeO3 in an electric transport experiment. Due to the presence of twinning in thin films we continue on this topic on single crystalline material. The pulsed laser deposition system maintained by the PhD student of the project was also used to optimize the growth of garnets with the help of visiting external students. Stemming from these side activities of we could demonstrate orbital currents in CuO-Pt-Tm3Fe5O12 heterostructures and could realize a tunable magnetic coupling in Y3Fe5O12 / Gd3Fe5O12 heterostructures. The coupling was demonstrated using volume-sensitive SQUID and surface-sensitive SMR measurements. It proved to be ferromagnetic concerning the iron sublattices, i.e., the magnetic structure was coherent across the interface. Spin Seebeck effect measurements appeared to be sensitive only to the top layer, which was GIG in our case. These measurements could confirm the presence of the ferromagnetic interlayer coupling between the two layers. Both of these later developments turned out to be very successful and are currently continued in the framework of our collaborative research center Spin+X.
Projektbezogene Publikationen (Auswahl)
- Harnessing non-local orbital-to-spin conversion of interfacial orbital currents for efficient spin-orbit torques. Phys. Rev. Lett. 125, 177201 (2020)
Shilei Ding, Andrew Ross, Dongwook Go, Lorenzo Baldrati, Zengyao Ren, Frank Freimuth, Sven Becker, Fabian Kammerbauer, Jinbo Yang, Gerhard Jakob, Yuriy Mokrousov, Mathias Kläui
(Siehe online unter https://doi.org/10.1103/physrevlett.125.177201) - Propagation Length of Antiferromagnetic Magnons Governed by Domain Configurations. Nano Lett. 20, 306 (2020)
Andrew Ross, Romain Lebrun, Olena Gomonay, Daniel Grave, Asaf Kay, Lorenzo Baldrati, Sven Becker, Alireza Qaiumzadeh, Camilo Ulloa, Gerhard Jakob, Florian Kronast, Jairo Sinova, Rembert Duine, Arne Brataas, Avner Rothschild, and Mathias Kläui
(Siehe online unter https://doi.org/10.1021/acs.nanolett.9b03837) - The challenge in realizing an exchange coupled BiFeO3-double perovskite bilayer. J. Magn. Magn. Mater. 506, 166766 (2020)
Sven Becker, Sven Heinz, Mehran Vafaee, Mathias Kläui, and Gerhard Jakob
(Siehe online unter https://doi.org/10.1016/j.jmmm.2020.166766) - Electrical detection of the spin reorientation transition in antiferromagnetic TmFeO3 thin films by spin Hall magnetoresistance. Phys. Rev. B 103, 024423 (2021)
Sven Becker, Andrew Ross, Romain Lebrun, Lorenzo Baldrati, Shilei Ding, Felix Schreiber, Franchesco Maccherozzi, Dirk Backes, Mathias Kläui, and Gerhard Jakob
(Siehe online unter https://doi.org/10.1103/physrevb.103.024423) - Magnetic coupling in Y3Fe5O12/Gd3Fe5O12 heterostructures. Phys. Rev. App. 16, 014047 (2021)
Sven Becker, Zengyao Ren, Felix Fuhrmann, Andrew Ross, Sally Lord, Shilei Ding, Rui Wu, Jinbo Yang, Jun Miao, Mathias Kläui, and Gerhard Jakob
(Siehe online unter https://doi.org/10.1103/physrevapplied.16.014047)
