Skyrmions in synthetic antiferromagnet nanorings for electrical signal generation

Abstract Current-driven magnetic skyrmions show promise as carriers of information bits in racetrack magnetic memory applications. Specifically, the utilization of skyrmions in synthetic antiferromagnetic (SAF) systems is highly attractive due to the potential to suppress the skyrmion Hall effect, which causes a transverse displacement of driven skyrmions relative to the shift direction. In this study, we demonstrate, through analytical calculations and micromagnetic simulations, that in the case of a nanoring geometry, current-driven skyrmions achieve a stable circular motion with a constant frequency, which is a prerequisite for a skyrmion-based clock device. Notably, the operational frequency in a SAF nanoring surpasses that in a bilayer ferromagnetic-heavy metal nanoring and lies in the GHz regime for current densities of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>40</mml:mn> <mml:mo>×</mml:mo> <mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> <mml:mrow> <mml:mtext>A</mml:mtext> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>m</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> . We also find that the performance of skyrmions in SAF nanorings is comparable to that of radial Néel domain walls for low current densities (approximately <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mn>30</mml:mn> <mml:mo>×</mml:mo> <mml:mrow> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> <mml:mrow> <mml:mtext>A</mml:mtext> </mml:mrow> <mml:mstyle scriptlevel="0"/> <mml:mrow> <mml:msup> <mml:mrow> <mml:mtext>m</mml:mtext> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:mrow> </mml:math> ) and low skyrmion densities ( N sk <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mo>≈</mml:mo> </mml:mrow> </mml:math> 6). Additionally, we introduce a novel skyrmionic three-phase AC alternator based on a SAF nanoring, which operates at frequencies in the GHz regime. Our findings underscore the potential of SAF nanorings as constituent materials in clock devices with tunable frequencies operating in the GHz regime.