Spin Transfer Oscillators for the THz regime

Spin-momentum transfer between a spin-polarized current and a ferromagnetic layer can induce steady-state magnetization precession, and has recently been proposed as a working principle for ubiquitous radio-frequency devices for radar and telecommunication applications.

We study new device structures that are potentially interesting for optimising the output signal quality of the spin-torque oscillators, but also allow for quantifying key magneto-transport parameters.

We focus on a one-of-a-kind fundamental study of the underlying physical mechanisms that govern the interplay between spin-polarized currents and magnetization, leading to both magnetoresistance effects and spin-transfer torques. The transfer of angular momentum from conduction electrons to the magnetization (known as “spin-transfer”) allows for a controlled manipulation of the magnetization via the injected currents. Furthermore, it exhibits advantageous scaling behaviour compared to conventional field-induced magnetization switching, thus paving the way for novel devices and applications.

Specifically, we target the area of oscillators functioning in the 100 GHz - 1 THz window. To this end, we use Mn-Ga-base alloys, due to their high perpendicular anisotropy and low magnetisation.

1."Effect of insertion layer on electrode properties in magnetic tunnel junctions with a zero-moment half-metal", A.Titova,C. Fowley, E. Clifford, Y-C.Lau,K. Borisov, D. Betto, G. Atcheson,R. Hübner, C. Xu, P. Stamenov, M. Coey, K. Rode, J. Lindner, J. Fassbender, A. Deac, Scientific Reports 9, 4020 (2019).

2. "A THz View on Magnetization Dynamics: Opportunities from the THz userfacility TELBE", N Awari; Z Wang; J-C Deinert; M Chen; B Green; S Germanskiy, I. Ilyakov, TVAG de Oliveira, A. Deac, S.Bonetti, M. Gensch, S. Kovalev, 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) (2019).

3. "Magnetocrystalline anisotropy and exchange probed by high-field anomalous Hall effect in fully compensated half-metallic Mn2RuxGa thin films", C. Fowley, K. Rode, Y-C. Lau, N. Thiyagarajah, D. Betto, K. Borisov, G. Atcheson, E. Kampert, Z. Wang, Y.Yuan, S. Zhou, J. Lindner, P. Stamenov, J. M. D. Coey, and A. Deac, Phys. Rev. B  98, 220406 (2018).

4. "Selective THz control of magnetic order: new opportunities from superradiant undulator sources", S. Kovalev, Z. Wang, J-C Deinert, N Awari, M Chen, B Green, S Germanskiy, T V A G de Oliveira, J S Lee, A Deac, D Turchinovich, N Stojanovic, S Eisebitt, I Radu, S Bonetti, T Kampfrath, M Gensch, J. Phys. D: Appl. Phys. 51, 114007 (2018).

5. "Tunnelling magnetoresistance of the half-metallic compensated ferrimagnet Mn2RuxGa", K. Borisov, D. Betto, Y.-C. Lau, C. Fowley, A. Titova, N. Thiyagarajah, G. Atcheson, J. Lindner, A. M. Deac, J. M. D. Coey, P. Stamenov, K. Rode, Appl. Phys. Lett. 108, 192407 (2016).

6. "Direct measurement of the magnetic anisotropy field in Mn–Ga and Mn–Co–Ga Heusler films", C. Fowley, S. Ouardi, T. Kubota, O. Yildirim, A. Neudert, K. Lenz, V. Sluka, J. Lindner, J. M. Law, S. Mizukami, G. H Fecher, C. Felser and A. M. Deac, J. Phys. D: Appl. Phys. 48, 164006 (2015).