Ultrafast magnetism and THz spectroscopy

Ferrimagnets such as GdFeCo can be switched by circularly polarized femtosecond laser pulses, opening the door to ultrafast magnetic data storage. We investigated this so-called all-optical switching (AOS) in TbFe [1]. We have shown that AOS also occurs in artificial zero moment magnets consisting of magnetic bilayers [2]. Previously, expensive and bulky laser amplifier systems were necessary to induce AOS. We have demonstrated AOS with a laser oscillator for the first time [3].

Ultrafast laser pulses can also induce spin currents in ferrimagnets. The spin current can be converted into a charge current at the interface to a non-magnetic material such as Pt via the inverse Spin-Hall effect. As a consequence, THz radiation is emitted by the transient charge current. We demonstrate that the ferrimagnets TbFe and GdFe show substantial THz emission with Pt on top [4, 5]. These so-called "spintronic emitters" can be easily fabricated by sputtering on the wafer scale and are robust and easy-to-use.

We show that spintronic THz emitters can also be witched on and off by chaning the temperature [6] or small magnetic fields [7].

[1] A. Hassdenteufel et al., Adv. Mat. 25, 3122 (2013)

[2] C. Schubert et al., Appl. Phys. Lett. 104, 082406 (2014)

[3] A. Hassdenteufel et al., Opt. Expr. 22, 10017 (2014)

[4] R. Schneider et al., ACS Photonics 5, 3936 (2018)

[5] R. Schneider et al.,  Appl. Phys. Lett. 115, 152401 (2019)

[6] M. Fix et al., Appl. Phys. Lett. 116, 012402 (2020)

[7] M. Fix et al., Appl. Phys. Lett. 117, 132407 (2020)