Why most of current induced spin orbit torques studies done on ultra thin Ferromagnetic systems? (i am talking about HeavyMetal (HM)/ Ferromagnet(FM)/ insulator or HM).
i have a qualitative understanding about Spin Hall effect and Rashba effects resulting in spin polarised currents from HM giving rise to SOT. But my confusion is about ultra thin limits of FM when PMA appears.
Is SOT assisted magnetization reversal seen only in ultra thin FM ? is it to do with the volume/ number of FM atoms to be reversed? or is it to do with the experimental ease of monitoring the magnetisation state of PMA systems?
It is an interface effect because the spin current induced, e.g., in a Pt film via the spin Hall effect stays only polarized over the spin diffusion length and second most applications aim at devices based on thin film heterostructures such as magnetic tunnel junctions. Those with perpendicular anisotropy are preferred as a consequence of demagnetizing fields contributing to the effective anisotropy.
As Christian said, this is an interface effect. The SOT, PMA , STT etc. effective fields in the FM layer averaged over its volume will be scaled as one over the FM layer thickness considering a pure macrospin behavior.
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