UC Riverside

Spin-based electronics or spintronics bear the potential to become an alternative paradigm to the traditional transistor-based electronics that is currently facing significant challenges related to energy efficiency, heat management and speed limitations. Understanding spin dynamics is essential for functionalizing spintronic devices. Frequency of operation of spintronic devices is in the range of GHz for ferromagnetic (FM) systems, and potentially THz for anti-ferromagnetic (AFM) systems.A segment of my research examines bilayer nanostructures comprising YIG and Ni for potential application in energy-efficient spintronic devices. Microwave emission spectroscopy performed on these hybrid magnetic nanodevices in perpendicular geometry showed the presence of auto-oscillatory mode driven by the spin-Seebeck effect– an effect that re-uses waste heat in the nanodevice to operate it. We further observed a substantial non-linear frequency shift at low magnetic fields. This work establishes a proof of concept for utilizing spin-based mechanisms in the pursuit of energy-efficient spintronics solutions. To push the boundaries of spin-based applications, AFM have been proposed. AFM operates in sub-terahertz to terahertz frequency range compared to FM at gigahertz frequency range. AFMs are also robust to external magnetic perturbations because of their zero net magnetization. In this dissertation, I translate the techniques and knowledge from FM systems to AFM systems and study the coherent spin dynamics in the bulk insulating antiferromagnetic systems. The magneto-resistive (MR) method is used to detect antiferromagnetic resonance (AFMR) in bulk Cr2O3 and Pt micro-structure device of size 10µm × 200µm. The successful detection of MR-AFMR set up the path to dive into the nanoscale AFM system. We achieved electrical detection of antiferromagnetic resonance signal in a nanodevice of dimension 200nm × 200nm. Additionally, we are also able to electrically detect the AFMR signal in Fe2O3/Pt AFM system. The analysis of the study of the AFMR signal and the angle between the microwave current flow and the c-axis of the anti-ferromagnetic device suggest that the resonance signal is dominated by the spin-torque excitation rather than inductive/Oersted excitation. The results of this work pave the road toward nanoscale AFM spin-torque devices and applications. As a prospect, we evaluate an alternative approach that relies on inductive excitation of AFM spin dynamics but is less restrictive to the miniaturized device size. We propose and develop integration of omega-shaped planar micro-resonator with micro-scale AFM structures. This work explores alternative pathways for hybrid AFM-superconductor systems and will broaden the experimental palette for the studies of AFM spin dynamics.