Size Dependence Effect in MgO-Based CoFeB Tunnel Junctions with Perpendicular Magnetic Anisotropy

We examine the effect of junction sizes on the magnetization reversal process and spin-transfer torque switching of the MgO-based CoFeB magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA). From the magnetic field transport measurements, it was found that the miniaturization of MTJs inherently enhances the switching asymmetry and the PMA of the soft layer. Our micromagnetic simulations confirmed that the dipolar field from the hard layer is responsible for the switching asymmetry and the increase in perpendicular shape anisotropy induces improvement of the PMA. It was further revealed that this additional anisotropy gained from the smaller MTJ sizes is not sufficient to sustain the thermal stability to meet the long-term information storage at the state-of-the-art complementary-metal-oxide semiconductor technology node. The pulsed spin-transfer torque measurements showed that a higher current density is needed to switch the magnetization of the soft layer in MTJ with smaller lateral dimensions, which is attributed to the increase in PMA. (C) 2012 The Japan Society of Applied Physics