Non-majority magnetic logic gates: a review of experiments and future prospects for 'shape-based' logic

We discuss the experimental demonstration of non-majority, two-input, nanomagnet logic (NML) AND and OR gates. While gate designs still can incorporate the symmetric, rounded-rectangle magnets used in the three-input majority gate experiments by Imre (2006 Science 311 205-8), our new designs also leverage magnets with an edge that has a well-defined 'slant'. In rectangular and ellipsoid nanomagnets, the easy axis of the device coincides with its longer edge. For a magnet with a slanted edge, the easy and hard axes are 'tilted', and magnetic fields applied along the (geometrical) hard axis alone can set the easy axis magnetization state. This switching phenomenon can be employed to realize NML Boolean logic gates with both reduced footprints and critical path delays. Experimental demonstrations of two-input AND and OR gates are supported by corresponding micromagnetic simulations with temperature effects associated with a 300 K environment. Simulations suggest that the time evolution of experimentally demonstrated structures is correct, and that designs can also tolerate clock field misalignment. Additionally, simulations suggest that a slanted-edge 'compute magnet' can (i) be driven by two anti-ferromagnetically ordered lines of NML devices (for input) and (ii) drive an anti-ferromagnetically ordered line (for output). Both are essential if slanted-edge devices are to be used in NML circuits. We conclude with a discussion of extensibility and scaling prospects for shape-based computation with nanomagnets.