Microstructure and phase dependence of magnetic properties of CoFeB nanowires

Arrays of amorphous CoFeB nanowires with the diameter of 250 nm and length of 20 mu m were fabricated by electrodepositing in pores of anodic aluminum oxide (AAO) templates. The corresponding changes of coercivity (H-c), remanence squareness (M-r/M-s), and the shape of hysteresis loops of NWs before and after annealing with the microstructure evolution have been investigated. The XRD and TEM results showed the precipitation of partial Co nanocrystallites and complete crystallization for the annealing treatment at 573 K and 773 K, respectively. The VSM results indicated a strong magnetic anisotropy in the amorphous nanowires and the easy magnetization axis was in perpendicular to the long wire axis. Both H-c and M-r/M-s increased with increasing annealing temperature. The magnetization reversal process occurred by the curling model for the amorphous nanowires and exhibited a transition for magnetization reversal after thermal annealing. In all, the magnetic properties of CoFeB nanowires can be controlled by tuning their microstructure with thermal annealing.