Oxidation and Annealing Process: Morphological Change and Nanocontact MR in Spin Valves With FeCo–AlO$_{x}$ NOL Spacer

摘要

We studied the formation mechanism of ferromagnetic nanocontacts (NCs) around 1–2 nm in diameter in thin AlO $_{x}$ nano-oxide layer (NOL) through in situ conductive atomic force microscopy (c-AFM), which is the only method suitable for measuring morphological changes in features this small. Spin valves (SVs) with Fe $_{0.5}$Co $_{0.5}$NCs in AlO $_{x}$ NOL fabricated by ion-assisted-oxidation (IAO) irradiated onto 1.3-nm-thick Al had nanocontact magnetoresistance (NCMR) characteristics with the MR ratio of 5% for 1 $Omega mu$m $^{2}$. According to measurements with c-AFM, these NCs were mostly located at the valleys between the AlO$_{rm x}$ grains or the edge of the grain. In other words, NCs were formed in the oxidation and cohesion process of Al by the IAO. Moreover, we found that the high-temperature annealing process improved the MR ratio to around 10% for 0.5 $Omega mu$m $^{2}$. The high-temperature annealing process may involve the AlO$_{x}$ morphological change and have led the Al atoms in NCs to migrate to AlO$_{x}$ by combining with oxygen as impurities. Then, the morphological changes and migration of Al caused NCs to be the low resistivity and the short length.