Abstract
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.
Highlights
Multilayered ferromagnetic materials have been the focus of extensive theoretical and experimental studies.[1,2,3,4,5,6] Especially, the discovery of giant magnetoresistance enhanced research interest in the interlay exchange coupling (IEC) between ferromagnetic layers separated by nonmagnetic spacers
Our numerical results demonstrate that currently available strong antiferromagnetic coupling, realized with an Ru or Ir layer, has the potential ability of increasing resonance frequency in the Synthetic antiferromagnets (SAFs) system with perpendicular anisotropy
Simulation results indicate that an opposite resonance frequency shift is induced when an external field is applied along the easy axis
Summary
Multilayered ferromagnetic materials have been the focus of extensive theoretical and experimental studies.[1,2,3,4,5,6] Especially, the discovery of giant magnetoresistance enhanced research interest in the interlay exchange coupling (IEC) between ferromagnetic layers separated by nonmagnetic spacers. Synthetic antiferromagnets (SAFs), consisting of antiparallel coupled ferromagnetic layers with the negative IEC, have increasingly drawn attention and inspire a research field of synthetic antiferromagnetic spintronics.[7,8] Representative industrial applications of the SAF are magnetic data storage and memory devices. The auto-oscillations of the SAF, excited by the spin transfer torque, lead to narrower resonance line widths compared with single layers.[14,15]. Another noteworthy property of the SAF is the markedly higher ferromagnetic resonance (FMR) frequency in the optic mode precession, as experimentally observed for in-plane magnetized bilayer structures and explained by an additional effective exchange field Jeff .16–20. We demonstrate reconfigurable resonance properties due to the bistable magnetization states, obtained with tuned material and structural parameters
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