The role of FeCo and FeCoCr nanowires array on the formation of single phase bi-magnets

Abstract Nanowire (NWs) arrays of FeCo and FeCoCr were prepared by AC pulsed electrodeposition embedded into an alumina template. They were then employed as an underlayer to provide the dot array of cobalt ferrite thin films. Highly ordered arrays of NWs with the diameter of 30 nm and length of 10 µm were fabricated and then annealed in various environments. The cobalt ferrite thin films were deposited by the sputtering approach with the almost constant thickness of 70 nm as the hard magnetic phase. The combination of FeCo and cobalt ferrite could provide an exchange spring magnet with the magnetic coupling feature. X-ray diffraction (XRD) patterns of the NW arrays indicated the formation of the body centered cubic (bcc) FeCo phase with [1 1 0] texture. Field emission electron microscopy (FESM) equipped by EDS also characterized the morphological features and elemental composition. Magnetization and coercivity of NWs were examined using the vibrating sample magnetometer. The maximum coercivity of NWs array is 2950 Oe which is related to H2 annealing FeCo NWs array. The magnetization reversal process of the as-deposited and annealed FeCo and FeCoCr NWs arrays was performed by angular dependence coercivity and squareness. Further, FORC diagrams indicated an interacting single domain behavior for as-deposited FeCo NWs and a weakly-interacting single domain state for the annealed samples. The morphological and structural features of cobalt ferrite were also studied by XRD, FE-SEM and AFM techniques. It was found that the cobalt ferrite dot array with a uniform chemical composition and structure was formed. The inter-diffusion of atoms between underlayer and thin films was confirmed by EDS. The maximum coercivity of the nanocompsite was 5800 Oe that is obtained for FeCoCr underlayer with argon annealing. The VSM analysis showed that sufficient exchange coupling was formed by using the FeCoCr underlayer in hydrogen annealing, while argon annealing provided a kink in the hysteresis loops. The obtained nanocomposites could be, therefore, considered as the potential candidate for use in the exchange spring magnet.