Ferromagnetic nano-conductive filament formed in Ni/TiO2/Pt resistive-switching memory

There is a question whether the conductive filament (CF) formed in the oxide layer of a resistive-switching random access memory is made of oxygen vacancies or metallic atoms. We investigated the CF of Ni/TiO2/Pt device using temperature coefficient of resistance (TCR), anisotropic magnetoresistance (AMR), and cross-sectional transmission electron microscopy with energy dispersive X-ray analysis (TEM-EDX). The low resistance state (LRS) of the device showed metallic property by TCR measurement. Furthermore, the device in the LRS showed AMR, which was a direct evidence of the formation of ferromagnetic CF. The cross-sectional TEM-EDX observation revealed that a nano-sized Ni precipitation existed in the area nearby a conductive spot. It is intensively suggested that Ni atoms migrated from the adjacent Ni electrode to TiO2 layer to form the nano-sized ferromagnetic CF.