Abstract-Enhanced detection sensitivity of terahertz magnetic nearfield with cryogenically-cooled magnetooptical sampling in terbium-gallium-garnet

Applied Physics Letters

Takayuki Kurihara,  Hongsong Qiu,   Kosaku Kato, Hiroshi Watanabe, Makoto Nakajima

https://aip.scitation.org/doi/abs/10.1063/1.5037521

Due to its efficient coupling with electron spins, the application of terahertz magnetic nearfield in metallic microstructures has been attracting attention. While paramagnetic materials that exhibit magneto-optical effect have been known to enable visualization of the terahertz magnetic fields (magneto-optical sampling), the low field-detection sensitivity has been setting a practical limit to the broader application of such a method. Here we propose and experimentally demonstrate that the terahertz magnetic nearfield-detection sensitivity of magneto-optical sampling with terbium-gallium-garnet crystal can be drastically enhanced by cooling the crystal down to cryogenic temperatures in accordance with Curie's law. Our result paves the way for the efficient characterization of the terahertz magnetic nearfield in planer metamaterials.

Abstract-Macroscopic magnetization control by symmetry breaking of photoinduced spin reorientation with intense terahertz magnetic-nearfield

Takayuki Kurihara, Hiroshi Watanabe, Makoto Nakajima, Shutaro Karube, Kenichi Oto, YoshiChika Otani, and Tohru Suemoto

https://journals.aps.org/prl/accepted/0507eY55R9418f66c77e9cc49d5b459f7e8379e96

We exploit intense terahertz (THz) magnetic nearfield to nonthermally drive the symmetry breaking process of the ground state spin order during optically-induced spin reorientation phase transition in ErFeO3. More than 80 % of total magnetisation in the sample have been macroscopically aligned to selectable orientations by the time delay between THz and optical pulses, reflecting the phase of coherent magnon and the direction of exciting magnetic nearfields. The spin dynamics are well reproduced by equation of motion including time-dependent magnetic potential. By using nonresonant excitation, we revealed the symmetry breaking process caused directly by THz magnetic field without spin precession.