Domain structure and reorientation in CoFe2O4

The microscopic processes underlying magnetostriction in ferrites were studied for the case of $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ single crystals by high-resolution in situ x-ray diffraction and complementary magnetic microscopy techniques. The data support the reports of Yang and Ren [Phys. Rev. B 77, 014407 (2008)] that magnetostriction in these materials originates from the switching of crystallographic domains, similar to ferroelastic or ferroelectric domain switching, and reveals the presence of two coexisting tetragonal spinel structures, corresponding to domains of high and of low strain. The latter alternate in the crystal, separated by 90\ifmmode^\circ\else\textdegree\fi{} domain boundaries, and can be explained by the effect of internal stress emerging during the transition into the ferrimagnetic phase. During magnetization of the sample two structural transitions are observed: a conversion of the transversal into axial domains at 1.95 kOe and a growth of the high-strain domains at the cost of the low-strain axial domains at 2.8 kOe. These microscopic changes are in good agreement with the macroscopic magnetization and magnetostriction behavior of $\mathrm{CoF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$.