We quantitatively compared film-level ferromagnetic resonance (FMR) measurements using standard vector network analyzer (VNA) techniques with device-level FMR measurements for both thermal FMR (T-FMR) and field-swept spin-torque FMR (FS-ST-FMR) techniques on magnetic tunnel junction (MTJ) thin films with in-plane magnetization. The film and FS-ST-FMR device determination of damping α are in agreement; however, α cannot be reliably determined by use of T-FMR device measurements due to bandwidth limitations. The device-level intercept of Hres vs. f is lower than film-level measurements of the effective magnetization (Meff) due to the demagnetizing field and exchange coupling of the patterned free layer. The intercept shows device-to-device variations due to a combination of size variation and local film variations. At the device level, the inhomogeneous broadening (ΔH0) is nearly zero, while in film-level measurements, μ0ΔH0 > 10 mT due to averaging of the local film variations detected explicitly in the intercept of Hres vs. f at the device level. These results suggest that continuous-film and FS-ST-FMR measurements on multiple devices can provide comparable information about thin-film Meff, α, and ΔH0 with minimal interpretation, but caution is necessary when using T-FMR to determine α or ΔH0.
Continuous-film vs. device-level ferromagnetic resonance in magnetic tunnel junction thin films
Eric R. Evarts, Matthew R. Pufall, William H. Rippard; Continuous-film vs. device-level ferromagnetic resonance in magnetic tunnel junction thin films. J. Appl. Phys. 28 February 2013; 113 (8): 083903. https://doi.org/10.1063/1.4793589
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