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Rapid Faraday Rotation on ε‑Iron Oxide Magnetic Nanoparticles by Visible and Terahertz Pulsed Light

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posted on 14.01.2019, 20:16 by Shin-ichi Ohkoshi, Kenta Imoto, Asuka Namai, Marie Yoshikiyo, Seiji Miyashita, Hongsong Qiu, Shodai Kimoto, Kosaku Kato, Makoto Nakajima
Light- or electromagnetic wave-responsive magnetism is an attractive issue in spin chemistry and optical materials science. Herein we show the magnetization reversal induced by visible-light pulsed laser and the ultrafast dynamic magneto­optical effect caused by terahertz (THz) pulsed laser irradiation onto chemically synthesized magnetic films based on gallium–titanium–cobalt-substituted ε-Fe2O3 (GTC-ε-Fe2O3) and ε-Fe2O3 nanoparticles. Visible-light pulsed laser irradiation switches the sign of the Faraday effect in GTC-ε-Fe2O3 films. On the other hand, irradiating the ε-Fe2O3 film with pulsed THz light induces an ultrafast Faraday rotation in an extremely short time of 400 fs. The time evolution dynamics of these ultrafast magneto­optical effects are theoretically demonstrated by stochastic Landau–Lifshitz–Gilbert calculations of a nanoparticle model that considers all motions of the individual spins. These ε-iron oxide magnetic nanomaterials are expected to contribute to high-density magnetic memory media or high-speed operation circuit magnetic devices.