Conductive Atomic Force Microscopy of Small Magnetic Tunnel Junctions With Interface Anisotropy

Magnetization reversal in CoFeB/MgO/CoFeB magnetic tunnel junctions with perpendicular magnetic anisotropy was studied as a function of both diameter (from 87 to 500 nm) and voltage (from -900 to 900 mV) using a conducting atomic force microscope. We found that the tunneling magnetoresistance near zero voltage was ~100% for all device sizes. The coercivity of the top CoFeB layer was identical within experimental error for the sizes between 158 and 500 nm but was smaller for 87 nm devices. This suggests a transition from domain-wall-nucleation-driven magnetization reversal to coherent rotation between 87 and 158 nm.