Introduction to broadband FMR spectroscopy

Todays and future technologies like magnetic memories, sensors, logics, and microwave signal processing are based on magnetic thin films. Attached research focuses on fundamental spintronics and magnonics with quasi-static techniques. These techniques use vibrating sample magnetometers (VSM) like the PPMS from Quantum Design to do for example magnetization hysteresis loop analysis. Additional probing of the microwave magnetization dynamics of thin films allows for additional material parameters to be measured, including gyromagnetic ratio (γ), damping (α), inhomogeneous broadening (ΔHo), exchange stiffness (A), etc.

Another measurement technique is FerroMagnetic Resonance (FMR) spectroscopy, which has been using microwave cavities on bulk samples since the late 1950s. However, such microwave cavities are often tuned to a single resonance frequency. Over the last decade, the development of broadband FMR spectroscopy, which uses either stripline [1] or coplanar waveguides, has allowed for measurements continuously spanning several 10s of GHz.

Such broadband measurements have provided significant improvements when it comes to precisely extracting the above material parameters. More specifically, broadband measurements are necessary for analyzing the frequency dependence of the resonance linewidth and distinguishing between intrinsic and extrinsic contributions to the magnetic damping. 

Find more information about the fundamental physics behind microwave magnetization dynamics, and on how broadband FMR measurements are performed and analyzed as well as several measurement examples using the FMR spectrometer from NanOsc Instruments AB in our application note about broadband FMR spectroscopy. 

[1] I. Maksymov and M. Kostylev, “Broadband stripline ferromagnetic resonance spectroscopy of ferromagnetic films, multilayers and nanostructures”, Physica E 69, 253 (2015).

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