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Capacitance effect on the oscillation and switching characteristics of spin torque oscillators.

Zeng T, Zhou Y, Leung CW, Lai PP, Pong PW - Nanoscale Res Lett (2014)

Bottom Line: The switching characteristic is featured with the emerging of the canted region; the canted region increases with the capacitance.When the external field is absent, the STO free-layer switching time exhibits different dependences on the capacitance for different injected current.These results help to establish the foundation for capacitance-involved STO modeling.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong.

ABSTRACT
We have studied the capacitance effect on the oscillation characteristics and the switching characteristics of the spin torque oscillators (STOs). We found that when the external field is applied, the STO oscillation frequency exhibits various dependences on the capacitance for injected current ranging from 8 to 20 mA. The switching characteristic is featured with the emerging of the canted region; the canted region increases with the capacitance. When the external field is absent, the STO free-layer switching time exhibits different dependences on the capacitance for different injected current. These results help to establish the foundation for capacitance-involved STO modeling.

No MeSH data available.


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STO free-layer magnetization switching time dependence on capacitance when (a)Idc = 7 mA and (b)Idc = 30 mA.
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Figure 7: STO free-layer magnetization switching time dependence on capacitance when (a)Idc = 7 mA and (b)Idc = 30 mA.

Mentions: Part A and Part B investigate the situation where the external field Happ is applied along the easy axis. In fact, for an in-plane magnetized STO in our system, the premises for a stable oscillation are the injected current and the external field. When the external field is absent, the injected current can only drive complete magnetization reversals from parallel state to anti-parallel. When a relatively small injected current (7 mA) is injected, the variation of STO resistance with the simulation time is shown in Figure 5a. It is found that capacitance can influence the free-layer magnetization switching time. Meanwhile, the trajectory in Figure 5b demonstrates that the existence of the capacitance renders plentiful unstable oscillating cycles before the final switching. It requires more oscillating cycles before final switching with increasing capacitance. When a relatively large injected current (30 mA) is injected, the variation of STO resistance with simulation time is shown in Figure 6. In this situation, the influence of capacitance on switching time is not obvious. The switching time is presented in Figure 7 with different capacitance values. The physical phenomena for STO free-layer switching time actually depends on three main factors: damping constant, in-plane spin torque component, and critical spin torque which intrigues the switching. In our study, we picked damping constant value 0.008, which is approach to the optimal value 0.013 for thin film switching. Thus we only consider the donation from the in-plane spin torque component and the critical spin torque which intrigues the switching. Based on the previous investigation [20], the switching time can be reasonably fitted by:


Capacitance effect on the oscillation and switching characteristics of spin torque oscillators.

Zeng T, Zhou Y, Leung CW, Lai PP, Pong PW - Nanoscale Res Lett (2014)

STO free-layer magnetization switching time dependence on capacitance when (a)Idc = 7 mA and (b)Idc = 30 mA.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4230906&req=5

Figure 7: STO free-layer magnetization switching time dependence on capacitance when (a)Idc = 7 mA and (b)Idc = 30 mA.
Mentions: Part A and Part B investigate the situation where the external field Happ is applied along the easy axis. In fact, for an in-plane magnetized STO in our system, the premises for a stable oscillation are the injected current and the external field. When the external field is absent, the injected current can only drive complete magnetization reversals from parallel state to anti-parallel. When a relatively small injected current (7 mA) is injected, the variation of STO resistance with the simulation time is shown in Figure 5a. It is found that capacitance can influence the free-layer magnetization switching time. Meanwhile, the trajectory in Figure 5b demonstrates that the existence of the capacitance renders plentiful unstable oscillating cycles before the final switching. It requires more oscillating cycles before final switching with increasing capacitance. When a relatively large injected current (30 mA) is injected, the variation of STO resistance with simulation time is shown in Figure 6. In this situation, the influence of capacitance on switching time is not obvious. The switching time is presented in Figure 7 with different capacitance values. The physical phenomena for STO free-layer switching time actually depends on three main factors: damping constant, in-plane spin torque component, and critical spin torque which intrigues the switching. In our study, we picked damping constant value 0.008, which is approach to the optimal value 0.013 for thin film switching. Thus we only consider the donation from the in-plane spin torque component and the critical spin torque which intrigues the switching. Based on the previous investigation [20], the switching time can be reasonably fitted by:

Bottom Line: The switching characteristic is featured with the emerging of the canted region; the canted region increases with the capacitance.When the external field is absent, the STO free-layer switching time exhibits different dependences on the capacitance for different injected current.These results help to establish the foundation for capacitance-involved STO modeling.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical and Electronic Engineering, The University of Hong Kong, Pokfulam, Hong Kong.

ABSTRACT
We have studied the capacitance effect on the oscillation characteristics and the switching characteristics of the spin torque oscillators (STOs). We found that when the external field is applied, the STO oscillation frequency exhibits various dependences on the capacitance for injected current ranging from 8 to 20 mA. The switching characteristic is featured with the emerging of the canted region; the canted region increases with the capacitance. When the external field is absent, the STO free-layer switching time exhibits different dependences on the capacitance for different injected current. These results help to establish the foundation for capacitance-involved STO modeling.

No MeSH data available.


Related in: MedlinePlus