Spin-torque-driven magnetization dynamics for neuromorphic functionality

With the ever-increasing demand for computationally demanding tasks and large scale memory, new information processing and storage technology is needed. Spintronics plays a key role in the development of faster, smaller, and more energy efficient technology. In this work, the focus lies on the electrical control of magnetization dynamics through spin-orbit torques and the exploration of their potential for enabling neuromorphic functionality. More specifically, unconventional spin-orbit torques and the coupling of spin-Hall nano-oscillators are explored. First, unconventional spin-orbit torque generation in the non-collinear antiferromagnet and altermagnet Mn₃Pt is explored. The thin film growth process is optimized based on the structural characterization, and the electrical transport properties. Spin-torque ferromagnetic-resonance reveals that unconventional spin-orbit torques, resulting from a spin polarization component along the current direction, are generated when current is applied along specific directions with respect to the crystal and magnetic order. Second, unconventional spin-orbit torque generation in CrPt₃ is studied. Spin-torque ferromagnetic-resonance and second harmonic Hall measurements of CrPt₃/Cu/Ni₈₁Fe₁₉ heterostructures reveal that unconventional field-like spin-orbit torques are generated in both ferrimagnetic and paramagnetic CrPt₃ films indicating that the magnetic ordering does not play a role in generating unconventional torques. Instead, numerical calculations reveal that the unconventional torques stem from indirect non-local spin-orbit torques and symmetry breaking at the CrPt₃/Cu interface. Third, micromagnetic simulations show that unconventional spin-orbit torques can be used to generate magnetic droplet solitons in a ferromagnet with perpendicular magnetic anisotropy without applying an in-plane magnetic field. Due to the non-local injection of spin-orbit torques, which differs from the typical spin-valve geometry, multiple magnetic droplets can be generated and annihilated using specific current pulses. Last, Pt/Ni₈₁Fe₁₉ spin-Hall nano-oscillators are fabricated on Si substrate. Injection-locking of the oscillations to an {\em rf} signal reveal that direct electrical coupling of two oscillators is unfeasible due to the low power generation of a spin-Hall nano-oscillator. However, the frequency behavior of two connected oscillators can be tuned using two voltage sources. In addition, a fabrication process for Pt/Ni₈₁Fe₁₉ oscillators on top of an Y₃Fe₅O₁₂ film that were grown on Gd₃Ga₅O₁₂ is developed. This is non-trivial as several challenges need to be overcome that are due to the electrically insulating and poor thermally conducting film and substrate.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Materials Science & Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Klause, Robin

Contributors dc:contributor

• Hoffmann, Axel F.
• Hoffmann, Axel F
• Cahill, David G
• Zuo, Jian-Min
• Rakheja, Shaloo

• Spintronics
• Magnetic This Films
• Spin-orbit Torques
• Magnetization Dynamics

Statement dc:rights

• Copyright 2025 Robin Klause

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/129895

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F129895