Observation and Control of Magnetic Order Dynamics by Terahertz Magnetic Nearfield (Springer Theses) 9789811687921, 9789811687938, 9811687927

Table of contents :
Supervisor’s Foreword
Peer-Reviewed Papers
Conference Contributions
Acknowledgements
Contents
1 Introduction
1.1 Terahertz (THz) Control of Magnetic System
1.1.1 THz Spectroscopy
1.1.2 Usage of Intense THz Electric Fields
1.1.3 Control of Spin Dynamics with THz Magnetic Fields
1.1.4 Spin Reorientation Phase Transition (SRPT)
1.2 Field Enhancement Using Metallic Subwavelength Structures
1.2.1 Plasmonic Enhancement in Metallic Structures and Metamaterials
1.2.2 Plasmonic Techniques in the THz Region
1.2.3 Split-Ring Resonator as a Tool for THz Magnetic Field Enhancement
1.3 Purpose of This Thesis and Outline
References
2 Background
2.1 Rare-earth Orthoferrites (RFeO3)
2.1.1 Basic Properties of Orthoferrite
2.1.2 Spin Configuration
2.1.3 Free-Energy Description of the Rotation-Type SRPT
2.1.4 Magnetic Resonance Modes
2.1.5 Temperature Dependence of FM Mode Resonance
2.2 Generation and Detection of THz Pulses
2.2.1 THz Time-Domain Spectroscopy (THz-TDS)
2.2.2 Generation of THz Waves via Optical Rectification
2.2.3 Generation of Intense THz Waves by Tilted Wave Front Technique
2.2.4 Detection of Magnetization Dynamics by Magnetooptical (MO) Effects
2.2.5 Detection of THz Waves by Electro-Optic (EO) Sampling
2.3 THz Magnetic Nearfields in Split-Ring Resonator (SRR)
2.3.1 Electric Excitation of Magnetic Resonance Mode in SRR
2.3.2 Usage of Field Enhancement Effects in THz-SRR
2.3.3 Coupling of SRR and THz Spin Resonance Mediated by Magnetic Nearfield
References
3 Resonant Enhancement of Spin Precession by SRR-induced Magnetic Nearfields and Interactive Energy Transfer
3.1 Sample Fabrication
3.1.1 Fabrication of Single-Crystal ErFeO3 (001) Plate with Floating-Zone Method
3.1.2 Optical Characterization of ErFeO3 Sample
3.1.3 Fabrication of SRR Structures
3.2 Experiment Configuration and Measurement Setup
3.3 Result 1: Resonant Enhancement of FM Mode Precession
3.3.1 Original Spin Precession Dynamics of FM-Mode Without SRR
3.3.2 Temperature-Tuning of FM-Mode Frequency Around SRR Resonance
3.3.3 Coupled LLG-LCR Resonance Model
3.4 Result 2: Interactive Energy Transfer Between SRR and Spin
3.5 Chapter Summary
References
4 Control of Macroscopic Magnetic Order Dynamics Using SRR-Enhanced THz Magnetic Fields
4.1 Background: Controlling the Path of Phase Transition by the Coherent Spin Precession
4.2 Motivation
4.3 Experiment Setup/Sample Properties
4.3.1 Design of the SRR Structure
4.3.2 Experimental Setup and Sample
4.4 Results
4.4.1 Temperature-Dependence of the THz-Induced Spin Precession
4.4.2 Creation of Macroscopic Magnetization by SRPT
4.4.3 Estimation of Tilt Angle of Spins
4.4.4 Incident THz Amplitude-Dependence of the Created Magnetization
4.4.5 Temperature-Dependence of the Created Magnetization
4.4.6 Contribution of SRR Magnetic Fields on the Process of Macroscopic Magnetization Formation
4.5 Chapter Summary
References
5 Numerical Simulation of the Macroscopic Domain Formation
5.1 Simulation of Magnetization Dynamics Using LLG Equation and Free Energy Model
5.1.1 2-Spin Free-Energy Model
5.1.2 Equilibrium Spin States
5.1.3 Temperature-Dependence of Spin Resonance Frequency
5.1.4 Spin Precession Excited by SRR Magnetic Fields
5.1.5 Simulation of Ultrafast Heating Process
5.1.6 Simulation of dt-Waveform
5.2 Mechanism of Domain Creation by THz Magnetic Fields
5.2.1 Comparison of t- and Dt-Waveforms
5.2.2 Spin Dynamics During Potential Reshaping
5.3 Chapter Summary
References
6 Conclusion
6.1 Summary
6.2 Future Remarks
References
Appendix Relation Between the s- and m-parameters
A.1 Hamiltonian of SRR and Spin Systems Without Interaction
A.2 Inclusion of Interaction Term into Total Hamiltonian
A.3 Retrieving s and m from the New Hamiltonian
A.4 Remark