Quenching of the initial ac Susceptibility in Single Domain Ni Nanobars

The ac susceptibility measurement probes the dynamic properties of a magnetic material, which is believed to consist of magnetization rotation and domain wall motion contributions. Here we report the observation of a complete quenching of the initial ac susceptibility for a single domain Ni nanobar array, when the ac field is aligned with the long axis of the bars. The vanishing of the susceptibility in one direction is a unique nanoscale phenomena, allowing an unambiguous determination of the magnetic state of the nanostructure and a clean separation of different contributions to its dynamic properties. For example, an unambiguous determination of the temperature dependent surface anisotropy energy is obtained when the field is applied perpendicular to the long axis. This research was conducted at the Center for Nanophase Materials Sciences, which is sponsored at Oak Ridge National Laboratory by the Office of Basic Energy Sciences, U.S. Department of Energy.