MRAM prototypes of many MegaByte capacity has already been built, and they are poised to enter the production lines. But new concepts of even much faster MRAMs are still emerging. One such idea is to use the so-called “Spin Torque Transfer” (STT) effect for toggling between the 0 and the 1 states of a memory cell. The STT effect was predicted theoretically in 1996 independently by J. Slonczewski and L. Berger.
(J. Slonczewski, JMMM 1996, L. Berger, PR B 1996) Spin transfer (J. Slonczewski, JMMM 1996, L. Berger, PR B 1996) S Torque on S Mx(MxM0) Ex:Cobalt/Copper/ Cobalt The transverse component of the spin current is absorbed and transferred to the total spin of the layer j M x (M x M0)
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The 01 and 10 switching of a STT memory cell can be done by sending short current pulses through the cell in opposite directions: (for detailed explanation, read the text in the next slide)
Novel effects and futuristic ideas: Spin Hall Effect: “Pure” spin current: Ordinary current: transport of charge “Pure spin current”: transport of spin Pure spin current is indeed a fascinating idea: No charge transfer – problems with inductance or capacitance do not exist any more… Zero power dissipation! But how such currents can be “generated”? The Spin Hall Effect may be too weak a source for practical applications, but at least it may be used for testing the idea…
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