Zero Field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet

Harry Waring, N A B Johansson, Ivan J. Vera-Marun, Thomas Thomson

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Antiferromagnets have considerable potential as spintronic materials. Their dynamic properties include resonant modes at frequencies higher than can be observed in conventional ferromagnetic materials. An alternative to single phase antiferromagnets are Synthetic Antiferromagnets (SAFs), engineered structures of exchange coupled ferromagnet/non-magnet/ferromagnet trilayers. SAFs have significant advantages due to the wide ranging tunability of their magnetic properties and inherent compatibility with current device technologies, such as those used for STT-MRAM production. Here we report the dynamic properties of fully compensated SAFs using broadband ferromagnetic resonance and demonstrate resonant optic modes in addition to the conventional acoustic (Kittel) mode. These optic modes possess the highest zero field frequencies observed in SAFs to date with resonances of 18 GHz and 21 GHz at the first and second peaks in antiferromagnetic RKKY coupling respectively. In contrast to previous SAF reports which focus only on the first RKKY AF coupling peak, we show that a higher optic mode frequency is obtained for the second antiferromagnetic coupling peak. We ascribe this to the smoother interfaces associated with a thicker non-magnetic layer. This demonstrates the importance of interface quality to achieving high frequency optic mode dynamics entering the sub-terahertz range.
Original languageEnglish
Article number034035
Number of pages10
JournalPhysical Review Applied
Issue number3
Publication statusPublished - 13 Mar 2020


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