Data is presented from experiments showing the growth of domain structures as a function of the reversal field for a sample of TbFeCo. Results have been obtained for a wide range of fields and reversal times. At low fields the initial growth structures are thread-like domains. As the reversal field is increased the growth structures become increasingly more dendritic eventually evolving into compact domains with relatively smooth boundaries at the highest fields. This work is discussed in terms of the dynamics of the distribution of the energy barriers to reversal. (C) 2003 Elsevier B. V. All rights reserved.