Magnetic Field Dependence of Ni Nanorod Brownian Relaxation

Abstract

AC magnetic susceptibility and optical transmission measurements were performed on Ni nanorod suspensions for ac and superimposed dc magnetic fields up to 9 mT. With the comparably large magnetic moment per nanorod, these field values correspond to Langevin parameters $\xi$ up to about 80. These wide range of $\xi$ values, the narrow size distribution, and the absence of Neel relaxation make these single-domain ferromagnetic nanorods ideally suited for the experimental verification of the dependence of the Brownian relaxation time on ac and dc magnetic fields. Consistent results for the magnetic moment m and the zero-field Brownian relaxation time $\tau _{B,0}$ were obtained for all measurement modalities and the valid field range of alternative models for the ac susceptibility was evaluated.