Regensburg 2025 – scientific programme

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MA: Fachverband Magnetismus

MA 3: Magnonics I

MA 3.10: Talk

Monday, March 17, 2025, 12:00–12:15, H18

Inductive noise spectroscopy of thermally excited magnons — Luise Holder¹, Richard Schlitz¹, Jamal Ben Youssef², Christian Runge¹, Akashdeep Kamra^3,4, William Legrand⁵, Hans Huebl^6,7,8, •Michaela Lammel¹, and Sebastian T.B. Goennenwein¹ — ¹Universität Konstanz, Konstanz — ²LabSTICC-CNRS, Université Bretagne Occidentale, Brest — ³RPTU Kaiserslautern-Landau, Kaiserslautern — ⁴Universidad Autónoma de Madrid, Madrid — ⁵CNRS, Institute Néel, Université Grenoble Alps, Grenoble — ⁶Walther-Meißner-Institut, Garching — ⁷Technische Universität München, Garching — ⁸Munich Center for Quantum Science and Technology, Munich

For the identification of non-classical (squeezed) magnon states, quantitative knowledge about thermal or vacuum fluctuations of the magnetization is essential. We show that thermal magnetization fluctuations of a ferromagnetic thin film can be sensitively characterized using inductive magnon noise spectroscopy (iMNS). Our broadband approach based on a coplanar waveguide and a commercial spectrum analyzer allows to detect the microwave emission of the equilibrium magnetization fluctuations relative to a cold microwave background. Modeling the response of the whole microwave system and comparing it quantitatively with low-power broadband ferromagnetic resonance measurements in linear response yields excellent agreement, which verifies the equilibrium character of the iMNS. Thus, our work establishes a purely inductive broadband access to the equilibrium properties of magnetization fluctuations.

Keywords: magnon; noise spectroscopy; fluctuations