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.

Highlights

  • Antiferromagnetic (AF) spintronics has recently become a key area of research to enhance the capabilities of spintronic devices [1,2]

  • We demonstrate that higher frequencies can be obtained for the zero-field optic mode using synthetic antiferromagnets (SAFs) with the structure Co0.2Fe0.6B0.2(5 nm)/Ru(tRu)/Co0.2Fe0.6B0.2(5 nm), where Ta(2 nm)/Co0.2Fe0.6B0.2(5 nm)/Ru (tRu) is the Ru layer thickness

  • We show that the second RKKY AF coupling peak supports faster precessional dynamics than the first peak and explore the correlation between Ru layer interface quality and interlayer coupling strength

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Summary

INTRODUCTION

Antiferromagnetic (AF) spintronics has recently become a key area of research to enhance the capabilities of spintronic devices [1,2]. For future device development, it is critical to consider miniaturization and heat management [9], which makes the application of large magnetic fields technically challenging It is desirable for magnetic materials to possess a very high self-bias, meaning no externally applied magnetic field is required to achieve higher resonance frequencies. Notable enhancements to the fr frequency were demonstrated by Li et al [37] who reported a zero-field optic mode resonance of 11.32 GHz. Further, SAFs fabricated using a range of ferromagnetic components have been explored including Ni-Fe [38], Co [39,40] and (Fe,Co)N [41]. We show that the second RKKY AF coupling peak supports faster precessional dynamics than the first peak and explore the correlation between Ru layer interface quality and interlayer coupling strength

SAMPLE PREPARATION AND CHARACTERIZATION
STATIC MAGNETIC PROPERTIES
DYNAMIC MAGNETIC PROPERTIES
MODELING
CONCLUSION
Thin-film sample preparation
Structure characterization
Magnetic measurements
Ferromagnetic resonance measurements
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