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Abhishek Sharma

What is the direction of STT out-of-plane component in MTJ


1.What is the direction of STT out-of-plane component in MTJ?

whether it is cross(M,m) or cross(m,M)?

M-fixed FM magnetization

m-free layer magnetization.

2. in MTJ at equilibrium due to dissipation less spin current which configuration is favoured, FM or AFM?


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    Samiran Ganguly

    1. The tool calculates it as m x M, if I recall correctly. However, M x m will just have a negative sign. It is then a matter of convention which definition is preferred, as long everything is consistent with that definition.

    2. In general, the magnetic configuration of an MTJ is influenced by a lot of other factors, including any remnant fields from other layers (its very difficult to cancel out magnetic interactions precisely in a real device). As for the equilibrium spin current, all in-plane or Slonczewski like torque is 0, only field like torque exists, in out of plane. In a normal MTJ, the energy barrier of the magnet is large enough that this term doesn't really do much, other than being one of the many magneto-spin interaction at equilibrium that together decide which direction is energetically favored. It does play a role in hindering/supporting the switching process during P->AP/ AP->P transitions, as usually experimentally observed. For details I'd invite you to look into Dr. Deepanjan Datta's illuminating MTJ paper in IEEE TED "Voltage Asymmetry  of  Spin Toruqe in Magnetic Tunnel Junctions" published in 2012.

    Note: personally I dislike the term dissipationless spin current, because it has the connotations of getting energy out of nothing (equilibrium spin currents do not switch a magnet) which fundamentally violates first law of thermodynamics. It is a catchy name used by some for a very special context. 


    Hope this answers your queries.



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