Structure and magnetic properties of Co/CoO core-shell nanowires

Cobalt nanowires with high coercivity have been synthesized via a solvothermal chemical process. A record high room-temperature coercivity value of 12.5~kOe has been measured in aligned Co nanowires with a diameter of about 15~nm and a mean length of 200~nm. When the surface of the Co nanowires were oxidized, exchange-bias (EB) was detected at low temperatures owing to the exchange coupling between the ferromagnetic (FM) Co core and the antiferromagnetic (AFM) CoO shell of the nanowires. EB fields of $\sim $2.0 kOe were measured at 10 K, along the parallel direction of nanowires. Manipulation and control of the EB in the nanowires may lead to a better understanding of the EB effect and the applications of the nanowires in for future permanent magnets and recording media.