Spintronic THz emitters with uniaxial and unidirectional magnetic anisotropy for field-free operation and electrical THz phase flipping

• Applicant: Professor Dr. Markus Meinert
• Subject Area: Experimental Condensed Matter Physics ; Electronic Semiconductors, Components and Circuits, Integrated Systems, Sensor Technology, Theoretical Electrical Engineering ; Synthesis and Properties of Functional Materials
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 513154775

Spintronic THz emitters (STE) driven by femtosecond-laser pulses provide gapless, ultrabroadband THz radiation with up to 30 THz. They can be operated as unstructured, large-area emitters with high power Ti:Sa oscillators. For cheap and compact setups, antenna-coupled emitters driven by focused fiber lasers are advantageous. Geometrically, they resemble to a large extent the conventional photoconductive (Auston) switches as sources of THz radiation. The main difference here is that Auston switches are biased with a voltage, whereas the STEs do not require an electrical field, however a magnetic field is required to stabilize the orientation of the magnetization of the ferromagnetic film. In miniaturized setups this is a clear disadvantage. Also, the STEs currently lack the ability for phase switching to enhance the detected signal with a lock-in technique by 6dB, which is easily available with Auston switches by flipping the bias voltage. In this proposal, we attempt to develop an STE stack with magnetic anisotropy that will render the application of a magnetic field obsolete. We will follow two approaches: on the one hand, we will make use of magnetic films with uniaxial magnetic anisotropy. On the other hand, we will investigate unidirectional anisotropy with exchange bias. The second approach is targeted towards emitters with a simple, fixed orientation of the magnetization and therefore of the THZ polarization. In contrast, the uniaxial anisotropy will serve as an enabler technology for microstructured emitters with an electrically switchable magnetization via spin-orbit torque. Thereby, we will develop an antenna-coupled STE with electrical phase flipping for applications in lock-in homodyne measurement systems and bring the feature set of the recently developed STEs closer to what is standard with conventional Auston switches.

• DFG Programme: Research Grants