Thema der Dissertation:
Spin torques at terahertz frequencies: From linear response to ultrafast control of magnetic order
Spin torques at terahertz frequencies: From linear response to ultrafast control of magnetic order
Abstract: Spintronics (short for: spin-based electronics) is an active research field, which focuses on the spin of electrons alongside their charge. In terms of fundamental research, spin dynamics and the interactions between spins and other degrees of freedom are highly interesting. On the other hand, spintronics has the potential for developing next-generation technologies with unprecedented efficiency and data storage capabilities. With rapid advances in information technology and data transmission, spintronic operations are likely required to proceed at terahertz (THz) frequencies, including the manipulation, transport and detection of spins.
Here, we address the mechanisms of ultrafast spin torques and their potential applications in magnetic materials. Our main tool for this goal are THz-pump optical-probe experiments, where single-cycle electromagnetic pulses with THz frequencies are used to excite magnetic thin films. The resulting sample response is probed by the polarization change of femtosecond optical pulses.
The focus lies on the metallic antiferromagnet (AFM) Mn2Au, which is a promising candidate for spintronics due to its high ordering temperature, terahertz spin dynamics and strong spin-orbit coupling. Remarkably, electric rather than magnetic fields can be used to control the magnetic order in this material through so called Néel spin-orbit torques (NSOTs), yet the dynamics of this process have remained elusive. In our experiments with thin films of magnetically prealigned Mn2Au, we observe signals that can be consistently attributed to a NSOT-driven magnon mode with a frequency of ≈ 0.6 THz. The non-linear mode dynamics suggest that spins are deflected by up to 30° from their initial orientation, which suggests potential for 90°-switching within picoseconds for only moderately increased field strengths.
Motivated by this prospect, we identify the key requirements to achieve and observe ultrafast switching in experiments: i) external control over the AFM spin order, ii) fully calibrated magneto-optical probes to access the spin dynamics, and iii) the increase of the electric field strength inside the AFM film. We show that, in an exchange-spring system Mn2Au|Py, with a thin ferromagnetic layer of Py (Permalloy, Ni80Fe20), the AFM order can be controlled by small external magnetic fields, which greatly simplifies the detection of magnetic signals and enables full calibration of the system’s magneto-optic response. Having fulfilled requirements i) and ii), the electric field inside the AFM is increased by microstructuring the film into resonant THz antennas. We find that antennas exposed to strong single-cycle pulses display permanent changes of the spin-order consistent with NSOT-switching. Finally, pump-probe experiments on exchange-spring antennas provide hallmarks of single-shot switching within only a few picoseconds. Our results therefore mark a milestone on the path towards antiferromagnetic spintronic devices operating at terahertz frequencies.
Here, we address the mechanisms of ultrafast spin torques and their potential applications in magnetic materials. Our main tool for this goal are THz-pump optical-probe experiments, where single-cycle electromagnetic pulses with THz frequencies are used to excite magnetic thin films. The resulting sample response is probed by the polarization change of femtosecond optical pulses.
The focus lies on the metallic antiferromagnet (AFM) Mn2Au, which is a promising candidate for spintronics due to its high ordering temperature, terahertz spin dynamics and strong spin-orbit coupling. Remarkably, electric rather than magnetic fields can be used to control the magnetic order in this material through so called Néel spin-orbit torques (NSOTs), yet the dynamics of this process have remained elusive. In our experiments with thin films of magnetically prealigned Mn2Au, we observe signals that can be consistently attributed to a NSOT-driven magnon mode with a frequency of ≈ 0.6 THz. The non-linear mode dynamics suggest that spins are deflected by up to 30° from their initial orientation, which suggests potential for 90°-switching within picoseconds for only moderately increased field strengths.
Motivated by this prospect, we identify the key requirements to achieve and observe ultrafast switching in experiments: i) external control over the AFM spin order, ii) fully calibrated magneto-optical probes to access the spin dynamics, and iii) the increase of the electric field strength inside the AFM film. We show that, in an exchange-spring system Mn2Au|Py, with a thin ferromagnetic layer of Py (Permalloy, Ni80Fe20), the AFM order can be controlled by small external magnetic fields, which greatly simplifies the detection of magnetic signals and enables full calibration of the system’s magneto-optic response. Having fulfilled requirements i) and ii), the electric field inside the AFM is increased by microstructuring the film into resonant THz antennas. We find that antennas exposed to strong single-cycle pulses display permanent changes of the spin-order consistent with NSOT-switching. Finally, pump-probe experiments on exchange-spring antennas provide hallmarks of single-shot switching within only a few picoseconds. Our results therefore mark a milestone on the path towards antiferromagnetic spintronic devices operating at terahertz frequencies.
Time & Location
May 16, 2025 | 05:00 PM
Hörsaal B (0.1.01)
(Fachbereich Physik, Arnimallee 14, 14195 Berlin)