The effects of annealing on the structure and magnetic properties of CoNi patterned nanowire arrays

NiCo alloy nanowire arrays were fabricated by using an electrochemical method in a porous anodic aluminum oxide (PAO) template. X-ray-diffraction results showed that there was a preferred orientation in the CoNi nanowire arrays with Ni content ranging from 0.2 to 0.8 in the as-electro-deposited state, while a random orientation was observed after the sample was heat treated in an argon atmosphere. When the shape anisotropy is very high in the sample, it is found that the squareness (Mr/Ms) of the hysteresis loops for the samples is only about 0.6 before annealing, but increases to about 0.9 after annealing. All the results are discussed qualitatively and an explanation for the magnetic reversal mechanism in terms of a localized magnetization model is given. As the CoNi alloy nanowire arrays have high bit densities, they can be used as perpendicular magnetic recording media of high-density quantum magnetic disks.