Developing New Techniques for Investigating Static and Dynamic Magnetic Degrees of Freedom

The origin of magnetism can be found in the purely quantum mechanical property of spin, an intrinsic form of angular momentum. Investigations into understanding and controlling the spin degree of freedom have driven condensed matter research for the better part of a century. Real-world applications of the spin-degree of freedom depend on a microscopic understanding of the underlying mechanisms that define the dynamic and static interactions of the magnetization with the material’s environment. Investigating new tools and techniques to probe the dynamics and statics of a magnetic material is thus a vital part in the design of new spin-based applications, and in developing an understanding of magnetization dynamics on a fundamental time scale.

This dissertation discusses three topics of research that focus on the development of techniques to study fundamental static and dynamic magnetic degrees of freedom. First, an unexpected sign flip in the Kerr response of a thin film manganite perovskite La_2/3Sr_1/3MnO₃ is investigated through the magneto-optical Kerr effect. By applying an external tensile strain to another La_2/3Sr_1/3MnO₃ thin film, the origin of the sign flip is linked to a strain modification of the electro-optic response. This section examines the strong link between the magnetic structure, electronic structure, and lattice in the La_2/3Sr_1/3MnO₃ system.

The second topic of research examines the role of magnetic interparticle interactions of superparamagnetic iron oxide nanoparticles (SPION) in the dynamics of DNA-origami hinges. Numerically calculated magnetic dipole interactions are added to the measured free energy distribution of DNA-origami hinges to determine the potential for hinge dynamics driven by the magnetic interaction. The results predict a potential for hinge latching due to an attractive magnetic dipole-dipole interaction between the attached SPIONs.

The final research topic of this dissertation details progress towards a material generic method of exciting magnetization dynamics with a GaAs Schottky interface. Here, a pulsed laser is used to generate carriers in GaAs that are swept away from the GaAs interface due to the Schottky contact. The resulting current generates an in-plane magnetic field pulse that can be used to drive magnetization dynamics in a neighboring magnetic layer. We examine the potential of this effect in two heterostructures: Fe/MgO/GaAs and Y₃Fe₅O₁₂/epoxy/GaAs. Time-resolved ferromagnetic resonance is observed in an Fe/MgO/GaAs heterostructure at room temperature as a result of the transient current pulse. Progress toward the material generic extension of the transient current driven dynamics is explored in a Y₃Fe₅O₁₂/epoxy/GaAs heterostructure. The low excitation intensity required to drive this effect in the GaAs makes this a potentially attractive technique for investigating magnetization dynamics in magnetic materials.