Magnetization reversal in electrodeposited CoNi/Cu multilayer nanowires

Magnetization reversal and superparamagnetic behavior in electrodeposited CoNi/Cu multilayer nanowires with the CoNi layer thicknesses t(CoNi) ranging from nanometer to micrometer scales were investigated using vibrating sample magnetometer (VSM) and superconducting quantum interference device (SQUID). The angular dependence of the magnetization measurements with respect to the wire axis shows that CoNi/Cu nanowires exhibit different magnetization reversal processes depending on t(CoNi). The reversal for nanowires with thin disk-shaped CoNi layers (nanometer thickness) is of coherent rotation type, while that for long rod shaped CoNi layers (micrometer thickness) is consistent with a combination of coherent rotation and curling modes. The coercivity of the nanowires measured at room temperature decreases when t(CoNi) decreases (< 7 nm) and becomes nearly zero when t(CoNi) further decreases (< 2 nm), indicating a superparamagnetic behavior in the thin CoNi layers.