applied sciences Review Measurement of the Resonant Magneto-Optical Kerr Effect Using a Free Electron Laser Shingo Yamamoto and Iwao Matsuda * Institute for Solid State Physics, The University of Tokyo, Kashiwa, Chiba 277-8581, Japan;
[email protected] * Correspondence:
[email protected]; Tel.: +81-(0)4-7136-3402 Academic Editor: Kiyoshi Ueda Received: 1 June 2017; Accepted: 21 June 2017; Published: 27 June 2017 Abstract: We present a new experimental magneto-optical system that uses soft X-rays and describe its extension to time-resolved measurements using a free electron laser (FEL). In measurements of the magneto-optical Kerr effect (MOKE), we tune the photon energy to the material absorption edge and thus induce the resonance effect required for the resonant MOKE (RMOKE). The method has the characteristics of element specificity, large Kerr rotation angle values when compared with the conventional MOKE using visible light, feasibility for M-edge, as well as L-edge measurements for 3d transition metals, the use of the linearly-polarized light and the capability for tracing magnetization dynamics in the subpicosecond timescale by the use of the FEL. The time-resolved (TR)-RMOKE with polarization analysis using FEL is compared with various experimental techniques for tracing magnetization dynamics. The method described here is promising for use in femtomagnetism research and for the development of ultrafast spintronics. Keywords: magneto-optical Kerr effect (MOKE); free electron laser; ultrafast spin dynamics 1. Introduction Femtomagnetism, which refers to magnetization dynamics on a femtosecond timescale, has been attracting research attention for more than two decades because of its fundamental physics and its potential for use in the development of novel spintronic devices [1].