Binary frequency shift keying modulation in spin torque oscillators with synthetic antiferromagnetic layer

Abstract

Antiferromagnets exhibit ultrafast magnetization precession, which has the potential to enable the development of terahertz spin torque nano-oscillators. By utilizing perpendicularly magnetized magnetic nanopillars with a synthetic antiferromagnetic (SAF) free layer, we have demonstrated through theoretical and numerical analysis that stable out-of-plane precession states can be achieved by applying current and an electric field. In the case of small current, the two magnetic layers of the SAF are in antiparallel alignment and rotate around the z-axis with the precession frequency decreasing as the current strength increases. When the current-induced spin torque is strong enough to fully overcome the antiferromagnetic coupling, the SAF free layer is driven into a scissor-like precession state around the z-axis with the frequency increasing with current. By selecting the appropriate combination of the current and electric field, the magnetization precession orbits and precession frequencies can be adjusted. These controllable procession orbits with tunable frequencies and fixed magnetization precession amplitude may be a promising candidate for implementing binary frequency shift keying modulation techniques.