Spintronic terahertz emitters exploiting uniaxial magnetic anisotropy for field-free emission and polarization control

Abstract

We explore the terahertz (THz) emission from CoFeB/Pt spintronic structures in the below-magnetic-saturation regime and reveal an orientation dependence in the emission, arising from in-plane uniaxial magnetic anisotropy (UMA) in the ferromagnetic layer. Maximizing the UMA during the film deposition process and aligning the applied magnetic field with the easy axis of the structure allow the THz emission to reach saturation under weaker applied fields. In addition, the THz emission amplitude remains at saturation levels when the applied field is removed. The development of CoFeB/Pt spintronic structures that can emit broadband THz pulses without the need for an applied magnetic field is beneficial to THz magneto-optical spectroscopy and facilitates the production of large-area spintronic emitters. Furthermore, by aligning the applied field along the hard axis of the structure, the linear polarization plane of the emitted THz radiation can be manipulated by changing the magnitude of the applied field. We, therefore, demonstrate THz polarization control without the need for mechanical rotation of external magnets.

High Efficiency and Flexible Modulation of Spintronic Terahertz Emitters in Synthetic Antiferromagnets

“…Various NM layer materials with strong spin–orbit coupling, such as nonmagnetic heavy metals, − antiferromagnets, − two-dimensional materials, − and topological insulators, − have been experimentally demonstrated to be able to generate strong THz signals. − The THz emission process in STEs is complex and involves various successive effects including spin generation, spin diffusion, spin decoherence, and spin–charge conversion. The layer structure and film quality also play a crucial role in determining the efficiency of THz emission. ,− Beigang et al have conducted investigations in Fe/Pt bilayers to understand the different roles of layer thickness, growth condition, substrate choice, and geometrical arrangement in the THz emission process based on the ISHE-based mechanism. Moreover, the impact of the FM/NM interface has also been examined, revealing that the interfacial spin-to-charge conversion mainly arises from the skew scattering of spin-polarized electrons at interface imperfections.…”