Title: Exploring antiferromagnetic resonances of NiO with frequency-domain THz spectroscopy

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Date: March 28, 2023
Time: 3:30 p.m. to 4:30 p.m.
Category: Seminar

Teresa Jeffrey

Abstract: The characterization and analysis of magnetization dynamics and magnetic damping of antiferromagnetic magnons is important in the field of antiferromagnetic spintronics. This is primarily because antiferromagnets have magnetic resonances in the THz range as compared to ferromagnetic resonance which tends to occur in the GHz range. In this work, we employ frequency-domain THz spectroscopy to explore the antiferromagnetic resonance frequency associated with monocrystalline NiO [1]. Specifically, a continuous- wave THz spectroscopy system is used to measure the antiferromagnetic resonance of three NiO cuts (111), (110), and (100). To find the absorption peak, a reference measurement is taken in addition to the NiO measurement. Raw data from the reference and NiO can be visually compared to see two effects: the THz system instrument response and Fabry-Perot interference pattern. During analysis, the instrument response and Fabry-Perot pattern are subtracted so that a clear absorption peak at the resonant frequency of NiO can be observed. An antiferromagnetic resonance, near 1 THz, is seen in each cut of NiO. Our results demonstrate the utility of working in the frequency domain to characterize antiferromagnetic materials that will be used eventually for ultrafast antiferromagnetic spintronic device technologies.

References: [1] Moriyama, Takahiro, et al., Physical Review Materials 3.5, 051402 (2019)


Mitra Subedi


The antiferromagnetic interlayer exchange field constant is one of the most important parameters in the study of synthetic antiferromagnetic multilayers. This is primarily due to an explicit dependence of resonance frequency on exchange field constant. In this study, we focus on the variation of the exchange field constant with respect to the thickness of ferromagnetic layer(permalloy) in bilayer, trilayer, and tetralayer synthetic antiferromagnets that are based on both permalloy and ruthenium. Experimental data is analyzed using static equilibria configurations that are obtained by modeling the synthetic antiferromagnets with the Landau–Lifshitz–Gilbert (LLG) equation. For higher permalloy thicknesses the exchange field constant tends to be the same for SAFM multilayers. For thinner permalloy thicknesses, discrepancies in the exchange field constants between bilayers, trilayers, and tetralayers hint at the importance of finite temperature effects that are not accounted for using the LLG equation. This finding provides a very good experimental foundation for further theoretical as well as experimental research in this direction. 


Jian Huang


March 2023