Zero-field Optic Mode Beyond 20 GHz in a Synthetic Antiferromagnet

Abstract

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/nonmagnet/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 Spin-transfer-torque magnetic random-access memory 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 and 21 GHz at the first and second peaks in antiferromagnetic Ruderman-Kittel-Kasuya-Yosida (RKKY) coupling, respectively. In contrast to previous SAF reports that focus only on the first RKKY antiferromagnetic 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 nonmagnetic layer. This demonstrates the importance of interface quality to achieving high-frequency optic mode dynamics entering the subterahertz range.

Quantum Engineering With Hybrid Magnonic Systems and Materials (Invited Paper)

“…Thus,the optical and acoustic magnon modes that are usually reported in SAFs are from bilayers. [135][136][137] The uniform optical and acoustic antiferromagnetic resonances frequencies of bilayers can modeled and obtained by linearizing a coupled pair of equations that are based on the Landau-Lifshitz-Gilbert (LLG) equation:…”

Anisotropic Magnon–Magnon Coupling in Synthetic Antiferromagnets

“…[8][9][10][11][12][13] Typically in the practical case of zero field, the resonance frequency of OM in SAF is higher than the acoustic mode 2 and can be tuned up to 20 GHz. 14 When applying a magnetic field in a certain range, the OM frequency reduces and AM frequency increases. 12 Once two modes approaching each other, they can be hybridized by the arising of the magnon-magnon coupling in SAF, which is analogous to the hybrid quantum system.…”

Structural and Magnetic Properties of Pt/Co/Mn-Based Multilayers

“…Furthermore, at low temperature such alloys may display a behavior similar to a spin glass [40]. We also point out that for low nominal Mn thickness values in some of our samples, there is the possibility that Mn layers have not been deposited in a perfectly homogeneous way and instead remained in the island-growth regime which is common for sputtered ultrathin films [41] and may affect the magnetic properties. Before a more in-depth investigation of the complex Mn thickness dependence, we now turn to the magnetic properties of Ta(2)/[Pt(1.5)/Co(x)/Mn(0.4)] 2 /Pt(1.5) with varying Co layer thickness x.…”