The Einstein-de Haas Effect in Yttrium Iron Garnet at Radio Frequencies

• Author / Creator

  Dunsmore, Michael G

• The Einstein-de Haas (EdH) effect was measured for the first time more than a century ago, and a classical theory of its operational principle existed many years before the first observation of the effect. EdH torques are generated by the time rate of change of angular momentum and represent the close relationship between magnetism and mechanical angular momentum. This work serves to build upon a trend of miniaturizing EdH experiments, thereby increasing the frequency that EdH torques are applied. The pursuit of extending EdH torques to higher frequency outlines a distinct benefit of the EdH effect: the torque scales linearly in magnitude with drive frequency. This linear scaling of EdH torques is in stark contrast with conventionally studied cross-product torques, which scale linearly with applied DC field and are frequency independent. The first measurement of the EdH effect featured torques that were of order one million times smaller than cross-product torques. Enabled by nanofabrication of mechanical torsional resonators, we have brought measurements of the EdH effect to the nanoscale, and subsequently to radio frequencies where EdH and cross-product torques are of similar magnitude.Single crystal disks of yttrium iron garnet (YIG) with vortex ground states were affixed to the nanofabricated torsional resonators. Owing to the distinct origin of EdH and cross-product torques, we were able to simultaneously measure the torques and observed relative differences in the signal phases as the field was swept. The DC field where EdH and cross-product torque signals intersect allows us to calculate the magnetomechanical ratio g′ for YIG: the first measurement of its kind. Our results yield g′ = 1.78 ± 0.16. The uniformity of driving fields allows for the extension of EdH torque measurements beyond the low field and ultimately beyond annihilation of the vortex state. EdH torques in intermediate and high field ranges serve as a sensitive probe of magnetic surface defects. Future directions of this work are presented with an emphasis on testing the limit of the linear increase of EdH torque with frequency. We suggest that a phase-lag with respect to the driving field will emerge for high enough mechanical frequencies that will signal the out-pacing of spin lattice relaxation times.

• Subjects / Keywords

  • Magnetism
  • Einstein-de Haas Effect
  • Yttrium Iron Garnet
  • Spin Mechanics
  • Nanomechanics

• Graduation date

  Fall 2022

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-yzw8-c336

• License

  This thesis is made available by the University of Alberta Library 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.