Ballistic magnetoresistance?

We review the published work on electric transport in metallic magnetic nanocontacts of sizes reaching a single atom. Considering fabrication methods exempt from mechanical instabilities, we find two experimental consensuses in magnetoresistance measurements. Firstly, magnetoresistance does not exceed a few tens of per cent in atomic size constrictions. We attribute these modest values to the significant number of opened conduction channels expected in contacts of 3D metals. Secondly, anisotropic magnetoresistance is observed for all types of samples, with amplitudes at least one order of magnitude larger than those found in bulk samples. Abrupt resistance changes with field angle confirm the occurrence of discrete anisotropic magnetoresistance levels. The effect is attributed to enhanced spin-orbit coupling at the atomic scale, resulting in possible opening or closure of conductance channels when varying the angle between current and applied magnetic field.