University of Illinois Urbana-Champaign

Atomic structure characterization for YIG/ permalloy heterostructures

Qian, Jiangchao

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https://hdl.handle.net/2142/124721

Description

Title
Atomic structure characterization for YIG/ permalloy heterostructures
Author(s)
Qian, Jiangchao
Issue Date
2024-05-02
Director of Research (if dissertation) or Advisor (if thesis)
Zuo, Jian-Min
Department of Study
Materials Science & Engineerng
Discipline
Materials Science & Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
M.S.
Degree Level
Thesis
Keyword(s)
  • YIG
  • Heterostructure
  • STEM
  • thin film
  • magnonics
  • interface
  • strain
Abstract
Yttrium Iron Garnet/Ferromagnetic (YIG/FM) heterostructures with strong interlayer magnon-magnon coupling have attracted significant interest for their potential in hybrid magnonic devices. The interaction between ferromagnetic resonance modes in the FM layer and perpendicular standing spin wave modes in YIG, enabled by interfacial exchange interactions, yields rich physical phenomena, such as coherent spin pumping, magnetically induced transparency, and the efficient excitation of short-wavelength spin waves. However, despite these technological advances, the fundamental physical mechanisms governing interfacial exchange coupling remain inadequately understood. Understanding the exchange mechanisms are vital for facilitating interactions between the magnetic systems. Here, we investigate the relationship between the atomic structure at the interfaces and their magnetic properties using aberration-corrected scanning transmission electron microscopy (STEM). We analyze the YIG/permalloy interface in samples prepared using different surface treatments, with and without surface ion milling. The results reveal unique hybrid modes in ion-milled samples, indicative of antiferromagnetic exchange coupling at the YIG/Py interface and highlight significant structural and electronic differences introduced by ion-milling. The observation of an oxygen-mediated super-exchange coupling mechanism suggests that the antiferromagnetic coupling in YIG/Py bilayers is predominantly driven by this mechanism. We reveal the position of interstitial atoms near the ion-milled YIG/Py interface from two projection zones. Distortions in the YIG surface crystal are observed, which are associated with these interstitial atoms. DFT simulations are used to provide insights into the complex interplay of interstitial atoms and crystal distortion at the YIG/Py interface, which has slight surface roughness. We exam interfacial strain distribution in ion-milled sample of the YIG/permalloy heterostructure. Our results show that surface interfacial strain is twice of the strain in bulk YIG. The detected high strain appears to overlap with areas of distortion. The observed Ni diffusion at the sharp interface support the existence of interstitial atoms.
Graduation Semester
2024-05
Type of Resource
Thesis
Copyright and License Information
Copyright 2024 Jiangchao Qian

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