Anomalous properties of sub-10-nm magnetic tunneling junctions

Magnetic logic devices have advantages of non-volatility, radiation hardness, scalability down to the sub-5-nm range, and three-dimensional (3D) integration capability. Despite these advantages, nanomagnetic applications for information processing are limited today. The main stumbling block is the inadequately high energy required to switch information states in the spin-based nanodevices. Recently, the spin-transfer torque (STT) effect has been introduced as a promising solution [1-2]. In STT magnetic tunneling junctions (MTJs), using a spin-polarized electric current to switch magnetic states has the potential to solve the energy problem. However, the switching current density on the order of 1 MA/cm² in the current STT-MTJ devices, with the smallest reported to date characteristic cross-sectional size on the order of 10 nm, still remains inadequately high for enabling a wide range of information processing applications [3-4]. For the technology to be competitive in the near future, it is critical to show that it could be favorably scaled into the sub-10-nm range. On a positive note, due to a new physics in this previously poorly explored size range, nanomagnetic devices may display promising characteristics that can make them superior to their semiconductor counterparts. In this size range, the underlying spin physics is due to the surface as much as it is due the volume. As a result, the effective thermal reservoir that absorbs spin excitations is substantially reduced, which in turn leads to a reduced spin damping and consequently to a reduced switching current density. Hence, the current study to understand the junction size dependence of the spin switching current is timely. This paper presents the key results of this study.