Torque magnetometry for concurrent acquisitions of magnetostatics & spin-dynamics

• Author / Creator

  Fani Sani, Fatemeh

• To fully utilize magnetic structures, a rich understanding of their physical properties and magnetic interactions is required. As device sizes shrink to the nanoscale, it is also important to acquire characterization information in the presence of inevitable intrinsic pinning sites. Nanomechanical torque magnetometry has been used for capturing the quasi-static magnetization of single, mesoscopic magnetic structures in a non-invasive way. We demonstrate the subtle effects of intrinsic pinning sites on magnetization characterization. Moreover, we study the important role of nanoscale defects by engineering artificial pinning sites on the sample surface. Separated artificial sites can work together to eliminate the effect of intrinsic pinning sites. Additionally, we perform ac magnetic susceptibility studies including the harmonics, from which non-linearities of magnetization response can be inferred. The ability to simultaneously record the equilibrium magnetic hysteresis and the spin excitations have been an experimental challenge. We demonstrate a down-mixing concept using a nanomechanical torque sensor that enables the concurrent measurements of dc net magnetization and of magnetic resonance spectra, in an individual magnetic structure and at room temperature. A desired magnetic torque component can be measured by adjusting the frequencies of perpendicular RF (or ac) drives in a broad frequency range (dc to GHz). We investigate ferrimagnetic resonances in a yttrium iron garnet (YIG) structure, nearly ideal case study due to its low ferrimagnetic resonance linewidths. An effective gyromagnetic ratio is assigned to some of the resonance modes and the ferromagnetic resonance mode couplings are observed within an individual structure. Together with micromagnetic simulations, additional physical insights are developed through the spectroscopic map of the YIG structure.

• Subjects / Keywords

  • Torque sensing
  • Magnetometry
  • Magnetic resonance

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3DZ03G0R

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.