Quoting the International Technology Roadmap for Semiconductors (ITRS) 2009 Emerging Research Devices section, 'Nanomagnetic logic (NML) has potential advantages relative to CMOS of being non-volatile, dense, low-power, and radiation-hard. Such magnetic elements are compatible with MRAM technology, which can provide input–output interfaces. Compatibility with MRAM also promises a natural integration of memory and logic. Nanomagnetic logic also appears to be scalable to the ultimate limit of using individual atomic spins.' This article reviews progress toward complete and reliable NML systems. More specifically, we (i) review experimental progress toward fundamental characteristics a device must possess if it is to be used in a digital system, (ii) consider how the NML design space may impact the system-level energy (especially when considering the clock needed to drive a computation), (iii) explain--using both the NML design space and a discussion of clocking as context—how reliable circuit operation may be achieved, (iv) highlight experimental efforts regarding CMOS friendly clock structures for NML systems, (v) explain how electrical I/O could be achieved, and (vi) conclude with a brief discussion of suitable architectures for this technology. Throughout the article, we attempt to identify important areas for future work.

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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.

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We present the current state-of-the-art of nanomagnetic logic (NML), which is one of the beyond-Moore device technologies being pursued within the SRC-NRI (Nanoelectronics Research Initiative). Advantages of NML include low power and non-volatility. We show that all key ingredients for NML architectures have been demonstratedincluding logic, fan-out, and on-chip clock structures. Input and output can be accomplished in a fashion similar to MRAM technology. As such, NML is CMOS compatible.

Lithographically defined magnets can process and move information in a cellular, locally interconn ected architecture. Wires, mat0rity gates, and inversion have all been demonstrated at room temperature! (Fig. la-c), and it is estimated that if 100 magnets switch 108 times/s, the magnets themselves would dissipate only about 0.1 Wo f power!. Local clock fields required for switching, as well as I/O, can be realized with CMOS circuitry.Energy differences between magnetization states can be large, and an external stimulus is required for logic re evaluation. Fig. 2-i depicts a line of magnets that are initially in a logically correct state. A magnetic field (clock) modulates a device's energy barrier by biasing a device along its hard axis against a preferred shape anisotropy . As the field is removed, magnets relax into a state in accordance with a new input ( Fig. 2-iii). Copper wires clad with ferromagnetic material on the sides and bottom can provide a magnetic field for on-chip, local control of Nanomagnet Logic (NML) circuits ( Fig. 3i. Devices have been switched experimentally with this setup3.All proposals for Boolean functions with NML have been majority gate based! or assumed magnets with a uniform shape4• While a majority gate can be more computationally powerful than an AND/OR gate, not all Boolean functions can be efficiently mapped to majority logic (e.g. XOR -il'i2 + i2 'i/)' Reducing a clocked majority gate to a 2-input AND/OR gate is possibleS by permanently making one input a logic 0 or logic 1. However, the fixed input must be carefully designed so that it does not overwhelm the middle compute magnet before other inputs arrive.Alternatively, magnet shape dependent switching properties have been proposed to perform Boolean logic6• If a magnet with a slanted edge (see Fig. 4 inset -here on upper left side) initially has a strong, positive, y-component of magnetization, and an external field (Hx) is applied from left-to-right along its hard axis and then removed, there is no My state change. If the initial y-component of magnetization is negative and the same field is applied, even with no Hy bias, there is an My state change. Micromagnetic simulation results in Fig. 4 illustrate both cases for a 50x75x25 nm3 supermalloy magnet. The My state transition can be explained by plotting a device's demagnetizing energy as a function of angle of magnetization (Fig. 5a). The peak is not centered at 0 degrees -as would be the case for a symmetric rounded rectangle magnet (also in Fig. 5a). As such, the device is already on one side of the barrier. Because of this shift, if a clocking field biases a slanted-edge compute magnet along its hard axis, and input magnets are in opposite states (so there is no net y-bias), the compute magnet has a preferr ed y-component of magnetization when the hard axis field is removed. Given either input combination, the compute magnet should relax to the same state (Fig. 5a). However, if the input magnets are in the same state, their y-directed fringing fields can determine the ...