Dynamic Roughening and Fluctuations of Dipolar Chains

Nonmagnetic particles in a carrier ferrofluid acquire an effective dipolarmoment when placed in an external magnetic field. This fact leads them to formchains that will roughen due to Brownian motion when the magnetic field isdecreased. We study this process through experiments, theory and simulations,three methods that agree on the scaling behavior over 5 orders of magnitude.The RMS width goes initially as $t^{1/2}$, then as $t^{1/4}$ before itsaturates. We show how these results complement existing results on polymerchains, and how the chain dynamics may be described by a recent non-Markovianformulation of anomalous diffusion.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let