  The magnetic dynamics of low-dimensional iron ion chains have been studied
with regards to the tunable finite-sized chain length using iron phthalocyanine
thin films. The deposition temperature varies the diffusion length during thin
film growth by limiting the average crystal size in the range from 40 to 110
nm. Using a method common for single chain magnets, the magnetic relaxation
time for each chain length is determined from temporal remanence data and fit
to a stretched exponential form in the temperature range below 5 K, the onset
for magnetic hysteresis. A temperature-independent master curve is generated by
scaling the remanence by its relaxation time to fit the energy barrier for spin
reversal, and the single spin relaxation time. The energy barrier of 95 K is
found to be independent of the chain length. In contrast, the single spin
relaxation time increases with longer chains from under 1 ps to 800 ps. We show
that thin films provide the nano-architecture to control magnetic relaxation
and a testbed to study finite-size effects in low-dimensional magnetic systems.
