Some spinel ferrites can be oxidized or transformed at moderate temperatures. Such modifications were carried out on thin films of mixed cobalt copper ferrites and maghemite, by heating small regions with a low-power laser spot applied for about 100 ns. The very simple laser heating process, which can be done directly with a conventional photolithographic machine, made it possible to generate two-dimensional magnetization heterogeneities in ferrimagnetic films. Such periodic structures could display the specific properties of magneto-photonic or magnonic crystals. (c) 2013 Elsevier B.V. All rights reserved.