28 August 2014 Dual-frequency ferromagnetic resonance to measure spin current coupling in multilayers
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Abstract
Spin pumping is a method for injecting a pure spin current into a non-magnetic metal (NM) by inducing precession of a neighboring ferromagnet (FM) at its ferromagnetic resonance frequency. A popular method to detect spin current uses the Inverse Spin Hall Effect (ISHE) to convert the spin current to a detectable charge current and hence a voltage. In order to better understand the role of time independent and high frequency contributions to spin pumping, we sought to detect we attempt to detect spin currents by using a second microwave frequency to detect changes in linewidth of a second ferromagnet due to the spin-torque induced by the spin current from the first ferromagnet. This dual resonance is achieved by pairing a custom broadband coplanar transmission line with the high-Q resonant cavity of a commercial electron paramagnetic resonance spectrometer. This technique is general enough that it should enable the investigation of spin currents in any FM-NM-FM system, for any orientation of external field, and is not sensitive to voltage artifacts often found in ISHE measurements. We find that the condition for simultaneous resonance generates a dc spin current that is too small to produce a measurable change in linewidth of the second ferromagnet, confirming the dominance of ac spin currents in linewidth enhancement measurements.
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Rohan Adur, Chunhui Du, Hailong Wang, Sergei A. Manuilov, Fengyuan Yang, P. Chris Hammel, "Dual-frequency ferromagnetic resonance to measure spin current coupling in multilayers", Proc. SPIE 9167, Spintronics VII, 91672J (28 August 2014); doi: 10.1117/12.2066174; https://doi.org/10.1117/12.2066174
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