Observation and Control of Magnetic Order Dynamics by Terahertz Magnetic Nearfield

This book explicates the optical controls of antiferromagnetic spins by intense terahertz (THz) electromagnetic waves. The book comprises two key components: (1) the experimental demonstration of the enhancement of a THz magnetic field using a split-ring resonator (SRR) and (2) the control of the direction of magnetization by using the enhanced THz magnetic field to break the symmetry of optically-induced phase transition. These make up the first step leading to future spintronics devices.

In the beginning of the book, the author reviews the basics of the ultrafast laser and nonlinear optical techniques as well as the previously achieved experiments to control spin dynamics by THz magnetic fields. In this context, a new experimental protocol is described, in which electron spins in a ferromagnetic material are redirected at the unprecedented level in cooperation with the enhanced THz magnetic field. Subsequently, the author demonstrates that the THz magnetic field is significantly amplified as a nearfield around the SRR structured metamaterial, which is implemented by measuring spin precession in a solid. At the end, the author presents the key experiment in which the amplified THz magnetic nearfield is applied to the weak ferromagnet ErFeO3 along with the femtosecond near-infrared pulse, demonstrating the successful control of symmetry breaking of the spin system due to coherent control of the optically-induced spin reorientation phase transition pathways.

The comprehensive introductory review in this book allows readers to overview state-of-the-art terahertz spectroscopic techniques. In addition, the skillful description of the experiments is highly informative for readers in ultrafast magnonics, ultrafast optics, terahertz technology and plasmonic science.

Auteur

Takayuki Kurihara, Research Fellow (Assistant Professor) at the Institute for Solid State Physics, The University of Tokyo, is an experimentalist in ultrafast laser physics. His work is concerned with the investigation of condensed matter at ultrafast timescales. His research interests include R&D of the ultrafast optical techniques, terahertz and infrared sources, ultrafast spintronics and other condensed-matter systems.

Dr. Kurihara received his bachelor's degree from the Department of Engineering, The University of Tokyo. Thereafter he joined the group led by Professor Tohru Suemoto, and received his master of science and Ph.D. degrees in science from the Department of Physics, The University of Tokyo, in 2013 and 2016, respectively. During his Ph.D. course, he was enrolled in The Advanced Leading Graduate Course for Photon Science, and awarded a JSPS fellowship. He has also received a number of the best presentation prizes and awards.

Contenu

1. Introduction1.1 Terahertz (THz) Control of a Magnetic System1.2 Field Enhancement Using Metallic Subwavelength Structures1.3 Purpose and Outline of This Thesis2. Technical Background2.1 Rare-Earth Orthoferrites (RFeO3)2.2 Generation and Detection of THz Pulses2.3 THz Magnetic Nearfields in a Split-Ring Resonator (SRR)3. Resonant Enhancement of Spin Precession by SRR-Induced Magnetic Nearfields and Interactive Energy Transfer3.1 Sample Fabrication3.2 Experiment Configuration and Measurement Setup3.3 Result 1: Resonant Enhancement of FM Mode Precession3.4 Result 2: Interactive Energy Transfer Between SRR and Spin3.5 Chapter Summary4. Control of Macroscopic Magnetic Order Dynamics Using SRR-Enhanced THz Magnetic Fields4.1 Background: Controlling the Path of Phase Transition by the Coherent Spin Precession4.2 Motivation4.3 Experiment Setup / Sample Properties4.4 Results4.5 Chapter Summary5. Numerical Simulation of the Macroscopic Domain Formation5.1 Brief Summary of Important Features Observed in Chapter 45.2 Simulation of Magnetization Dynamics Using LLG Equation and Free- Energy Model5.3 Mechanism of Domain Creation by THz Magnetic Fields5.4 Chapter Summary6. Conclusion6.1 Summary6.2 Future ProspectsAppendix. Relation Between the s- and m- Parameters