Phase stability of Co nanowires prepared by electrodeposition via AAO templates

Cobalt nanowires with average diameters of 40 nm, 55 nm, 70 nm, 90 nm, 250 nm were prepared by electrodeposition using anodic aluminum oxide (AAO) templates. The as-deposited Co nanowires were dense and presented hcp monocrystal structure. Austenite transformation finish (Af) temperature of the nanowires was investigated with in-situ XRD. Af temperature of nanowires with diameter of 250 nm was found almost the same as bulk Co. While, there was a sudden dramatic increase (over 300 K) in Af temperature when the diameter decreased from 90 nm to 70 nm, gaining a great enhancement in the stability of hcp phase. However, Af temperature decreased slightly when the diameter became smaller than 70 nm. Possible reasons of this phenomenon were discussed.