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

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 Ω μm
²
. According to measurements with c-AFM, these NCs were mostly located at the valleys between the AlO
_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 Ω μm
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.