Self-organized growth of nanometric pyramids in ferrimagnetic epitaxial CoCr2O4 films

Self-organized pyramidal islands of ferrimagnetic spinel CoCr2O4 were epitaxially grown on MgAl2O4 (0 0 1). The surfaces of the islands are {1 1 1} facets, so they can be considered as true three-dimensional objects. Important characteristics of the structures can be tuned by varying growth parameters. Pyramids form above a critical thickness, and the existing granular-like underlying film grow later at a reduced rate. We discuss on the growth mechanism of pyramids and we end comparing the CoCr2O4 pyramids with the widely investigated Si-Ge dots.