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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.


Related in: MedlinePlus

When Happ = 0.05 T, the frequency dependence on capacitance when (a)Idc = 8 mA, (b)Idc = 9 mA, (c)Idc = 12 mA, and (d)Idc = 20 mA.
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Figure 2: When Happ = 0.05 T, the frequency dependence on capacitance when (a)Idc = 8 mA, (b)Idc = 9 mA, (c)Idc = 12 mA, and (d)Idc = 20 mA.

Mentions: The oscillation characteristics are studied when external field is applied along the easy axis (x-axis) with the value Happ =0.05 T. When Idc is applied, the free layer of the STO is in a steady precessional state where a stable frequency is induced. The presence of a parallel connected capacitor shares the injected dc current with the STO, which changes the free-layer magnetization precessional state to a new orbit. The STO oscillation frequencies are presented under different capacitance values in Figure 2. ‘Opposite sign’, ‘Same sign’, and ‘GMR type’ refer to frequency vs capacitance curves when β = −10%, β =10%, and β =0%, respectively. When the injected current Idc is relatively small (8 and 9 mA) and the field-like term is ignored (β =0%), the increase of the capacitance leads to the general decrease of the oscillation frequency, as shown in Figure 2a,b. When the capacitance is in the range of 0.01 to 0.1 pF, this negative correlation is enhanced for β = −10% whereas it changes to positive correlation for β =10%. Meanwhile, when the capacitance is in the range of 1 to 100 pF, this negative correlation is enhanced for β =10% whereas it changes to positive correlation for β = −10%. This phenomenon is due to the fact that the field-like term is dependent on the applied bias voltage [12,16,17]. Either relatively small capacitance value or relatively large capacitance value would result in a large change of the bias voltage, which also induce a large change of the field-like term. When Idc reaches the value of 12 mA, a ‘V-shape’ trend formed between the frequency and the capacitance. Compared with the minimum peak for β =0%, the minimum peak for β = −10% occurs at lower capacitance value while it occurs at higher capacitance value for β =10%, as shown in Figure 2c. When Idc reaches the value of 20 mA, general positive correlation between the capacitance and the frequency is exhibited for β = −10%, β =10%, and β =0%. The field-like term (either β = −10% or β =10%) can result in higher oscillation frequency in this case.


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)

When Happ = 0.05 T, the frequency dependence on capacitance when (a)Idc = 8 mA, (b)Idc = 9 mA, (c)Idc = 12 mA, and (d)Idc = 20 mA.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

Figure 2: When Happ = 0.05 T, the frequency dependence on capacitance when (a)Idc = 8 mA, (b)Idc = 9 mA, (c)Idc = 12 mA, and (d)Idc = 20 mA.
Mentions: The oscillation characteristics are studied when external field is applied along the easy axis (x-axis) with the value Happ =0.05 T. When Idc is applied, the free layer of the STO is in a steady precessional state where a stable frequency is induced. The presence of a parallel connected capacitor shares the injected dc current with the STO, which changes the free-layer magnetization precessional state to a new orbit. The STO oscillation frequencies are presented under different capacitance values in Figure 2. ‘Opposite sign’, ‘Same sign’, and ‘GMR type’ refer to frequency vs capacitance curves when β = −10%, β =10%, and β =0%, respectively. When the injected current Idc is relatively small (8 and 9 mA) and the field-like term is ignored (β =0%), the increase of the capacitance leads to the general decrease of the oscillation frequency, as shown in Figure 2a,b. When the capacitance is in the range of 0.01 to 0.1 pF, this negative correlation is enhanced for β = −10% whereas it changes to positive correlation for β =10%. Meanwhile, when the capacitance is in the range of 1 to 100 pF, this negative correlation is enhanced for β =10% whereas it changes to positive correlation for β = −10%. This phenomenon is due to the fact that the field-like term is dependent on the applied bias voltage [12,16,17]. Either relatively small capacitance value or relatively large capacitance value would result in a large change of the bias voltage, which also induce a large change of the field-like term. When Idc reaches the value of 12 mA, a ‘V-shape’ trend formed between the frequency and the capacitance. Compared with the minimum peak for β =0%, the minimum peak for β = −10% occurs at lower capacitance value while it occurs at higher capacitance value for β =10%, as shown in Figure 2c. When Idc reaches the value of 20 mA, general positive correlation between the capacitance and the frequency is exhibited for β = −10%, β =10%, and β =0%. The field-like term (either β = −10% or β =10%) can result in higher oscillation frequency in this case.

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