Under different nanomagnets' size, switching behaviour of all spin logic (ASL) devices constructed with Co and permalloy (Py) nanomagnets are studied by using the coupled spin-transport/magneto-dynamics model. The results indicate that ASL devices' switching delay and energy dissipation can be reduced by decreasing the thickness of nanomagnets. The switching delay and energy dissipation of PyASL are lower than those of CoASL in a smaller thickness of nanomagnet, but they increase much faster than those of CoASL when the nanomagnets (FM) thickness increases. With the dimensional scaling of nanomagnets, the ASL devices' switching delay and energy dissipation decrease rapidly and the influence of thermal noise become weak. Moreover, under the same nanomagnet volume, ASL devices' switching delay, energy dissipation, and energy barrier can be reduced by decreasing aspect ratio. These findings can provide guidelines for optimising the ASL devices' materials and size.

The need for low-power alternatives to digital electronic circuits has aroused the increasing interest in spintronic devices for their potentials to overcome the power and performance limitations of (CMOS). In particular, all spin logic (ASL) technology, which stores information using the magnetization direction of the nano-magnet and communicates using spin current, is generally thought to be a good post-CMOS candidate for possessing capabilities such as nonvolatiliy, high density, low energy dissipation. In this paper, based on nano-magnetic dynamics described by Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation and transport physics of spin injection and spin diffusion, a coupled spin-transport/magneto-dynamics model for ASL is established. Under different channel lengths and applied voltages, the switching characteristics of ASL device comprised of Co and Permalloy (Py) nano-magnets are analyzed by using the coupled spin-transport/magneto-dynamics model. The results indicate that the switch delay, energy dissipation and thermal noise effect of PyASL are lower than those of CoASL. The main reason is that the saturation magnetization of Py is less than that of Co. Under the same applied voltage, the maximal channel length of PyASL is longer than that of CoASL when ASL device can switch accurately. Moreover, the two ASL devices' switching delay can be reduced by reducing channel length or increasing applied voltage, and the energy dissipation can be reduced by reducing channel length or applied voltage, whereas there are no optimized applied voltages to minimize the energy-delay product. In addition, the influences of thermal noise on switching delay and energy dissipation can be improved by lowering channel length, but increasing applied voltage can only improve the influence of thermal noise on switching delay. The above-mentioned conclusions will supply essential guidelines for optimizing the ASL devices' materials and configuration.