Experiments on a nearly spin degenerate two-dimensional electron system
reveals unusual hysteretic and relaxational transport in the fractional quantum
Hall effect regime. The transition between the spin-polarized (with fill
fraction ν=1/3) and spin-unpolarized (ν=2/5) states is accompanied
by a complicated series of hysteresis loops reminiscent of a classical
ferromagnet. In correlation with the hysteresis, magnetoresistance can either
grow or decay logarithmically in time with remarkable persistence and does not
saturate. In contrast to the established models of relaxation, the relaxation
rate exhibits an anomalous divergence as temperature is reduced. These results
indicate the presence of novel two-dimensional ferromagnetism with a
complicated magnetic domain dynamic.Comment: 15 pages, 5 figure