Numerical analysis of the spin dynamics in bilayer nanodots with interlayer antiferromagnetic coupling

Synthetic antiferromagnetic nanodots with perpendicular magnetic anisotropy are promising candidates for improving the performance of magnetic random-access memory or spin torque nano-oscillators; however, the mechanism for the interlayer antiferromagnetic coupling is still not completely understood. Therefore, we numerically investigated the ferromagnetic resonance characteristics of perpendicularly magnetized bilayer nanodots with interlayer antiferromagnetic coupling. The results show that the resonance frequency strongly depends on the interlayer antiferromagnetic coupling intensity and the individual layer thickness. It was found that external fields induce opposite resonance peak shifts, reflecting the contradicting Zeeman energy effect on individual layers with opposite magnetization directions. The resonance properties were successfully reconfigured by adjusting the uniaxial anisotropy and coupling intensity. Moreover, bistable (parallel and antiparallel) magnetization states were controlled by applying an external field sweep. The difference between the resonance frequencies of two bistable states was enhanced by decreasing the layer thickness and increasing the antiferromagnetic coupling intensity. Our numerical results demonstrate the potential ability of currently available strong interlayer exchange coupling for further increasing of high resonance frequencies in the synthetic antiferromagnet system with perpendicular anisotropy.