Author Topic: bias voltages  (Read 3769 times)

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Offline lhwang6929

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bias voltages
« on: December 24, 2008, 03:46 »
dear all:
  There is speaking in VNL mannul"For high bias voltages the linear-response approximation is no longer valid",I want to ask, generally speaking how high bias voltages is  high?

Offline Nordland

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Re: bias voltages
« Reply #1 on: December 24, 2008, 12:32 »
I guess it is matter of opinion and to what degree one can accept the approximation of the linear-response approximation.
I have done two cases studies of it once, I will try to see if I can find them, however I remember a couple of things for sure.

If the system you are calculating on, is typical standard system without spin polarization and perhaps have ohmic resistance,
then it goes something like this.
Quote
0-0.2 V Technical no deviation.
0.2V-0.4V Small deviation, but still within the model precision.
0.4V-0.7V Slightly deviation, but still shows the same behavior
0.7V-1.0V The deviation becomes more than 10-20%, and this could be considered high bias.
1.0V -      Typical large errors.
However if the target systems is a MTJ's (Magneto-Tunnel-Junction) like FeMgOFe, where you want to understand the details of the spin current
in order to calculate the spin-torque etc, then I would set 0.3 V as a "high voltage".

But there are no need to despair, since one can always use the fully selfconsistent calculate current functionality to get the right results.
Now I will go look, if I can find my case studies on this matter.






Offline lhwang6929

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Re: bias voltages
« Reply #2 on: December 25, 2008, 03:41 »
Thanks a lot!

Offline Nordland

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Re: bias voltages
« Reply #3 on: December 26, 2008, 11:23 »
I found this test example for Li-H2-Li, where I compare the Linear Response Current in ATK with the fully selfconsistent current from ATK.

I have attached the graph.