Ultrafast heat-assisted control of spins in ferrimagnetic dielectrics

This thesis investigates ultrafast optical control of spin dynamics in ferrimagnetic and canted antiferromagnetic dielectrics - materials that offer promising avenues for future optical data storage technologies. In particular, we study heat-assisted magnetic switching and all-optical control of magnetization, focusing on how these effects depend on laser parameters, temperature, and magnetic field.
We begin by outlining the fundamental principles of magnetism and light-matter interaction, emphasizing magneto-optical and opto-magnetic effects. The experimental methods are based on time-resolved pump-probe techniques employing the magneto-optical Faraday effect with femtosecond resolution. We use magneto-optical diffraction of visible light to probe domain wall motion with nanometer spatial and sub-picosecond temporal resolution. In ferrimagnetic garnets, we analyze heat-assisted switching and identify a narrow range of conditions enabling recording-size precession amplitudes. Our simulations reveal that this regime corresponds to an optimal energy barrier between magnetic states. In orthoferrites, we explore coherent control of spin reorientation using double-pulse excitation. We identify temporal windows of spin insensitivity related to strong damping near the phase transition. Finally, we study the full polarization dependence of the switching, demonstrating that its dynamics defy simple additive behavior. These findings provide new insight into ultrafast spin control and support the development of THz-speed magneto-photonic devices.