Darren M. Graham
Spintronic terahertz (THz) emitters have demonstrated high electric field amplitudes [1, 2], a broad spectral bandwidth with gapless coverage [3, 4], and they produce linearly polarized radiation aligned perpendicular to the magnetization of the structures. The latter characteristic offers the possibility to create devices in which the THz amplitude and polarization can be controlled through careful magnetic manipulation [5, 6]. It also offers a unique means to control the emission through the exploitation of magnetic anisotropy.
In this talk, I will present our work investigating the THz emission from CoFeB/Pt spintronic structures in the below-magnetic-saturation regime and discuss how we enhanced the in-plane uniaxial magnetic anisotropy (UMA) in the ferromagnetic layer by varying the sputter deposition conditions. In the case of a ferromagnetic film with a UMA, we find that alignment of a magnetic field along the easy axis enables the THz emission to remain at saturation levels when the magnetic field is subsequently removed, thus realizing field-free THz emission. Furthermore, we demonstrate that the UMA can be exploited to enable control of the polarization of the emitted THz pulse. By applying the magnetic field along the hard axis, we achieve rotation of the plane of linear polarization by varying the magnitude of the applied magnetic field.
Exploitation of UMA can provide polarization control and spintronic structures that can emit broadband THz radiation without the need for an applied magnetic field. This has applications in THz magneto-optical spectroscopy and facilitates the production of large-area spintronic emitters.
References:
[1] T. Seifert, S. Jaiswal, M. Sajadi, G. Jakob, S. Winnerl, M. Wolf, M. Kläui, and T. Kampfrath, Appl. Phys. Lett. 110, 252402 (2017). [2] R. Rouzegar, A. L. Chekhov, Y. Behovits, B. R. Serrano, M. A. Syskaki, C. H. Lambert, D. Engel, U. Martens, M. Münzenberg, M. Wolf, G. Jakob, M. Kläui, T.S. Seifert, and T. Kampfrath, Phys. Rev. Appl. 19, 034018 (2023). [3] C. Bull, S. M. Hewett, R. Ji, C.-H. Lin, T. Thomson, D. M. Graham, and P. W. Nutter, APL Mater. 9, 090701 (2021). [4] T. Seifert, S. Jaiswal, U. Martens, J. Hannegan, L. Braun, P. Maldonado, F. Freimuth, A. Kronenberg, J. Henrizi, I. Radu, E. Beaurepaire, Y. Mokrousov, P. M. Oppeneer, M. Jourdan, G. Jakob, D. Turchinovich, L. M. Hayden, M. Wolf, M. Münzenberg, M. Kläui, and T. Kampfrath, Nat. Photonics 10, 483 (2016). [5] M. T. Hibberd, D. S. Lake, N. A. B. Johansson, T. Thomson, S. P. Jamison, and D. M. Graham, Appl. Phys. Lett. 114, 031101 (2019). [6] H. Niwa, N. Yoshikawa, M. Kawaguchi, M. Hayashi, and R. Shimano, Opt. Express 29, 13331 (2021).