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...