Local structure distortion and spin Hamiltonian parameters for Cr4+ ions in Cr4+:alpha-Al2O3 crystals

The relations between the spin Hamiltonian (SH) parameters and crystal structure of Cr(4+):alpha-Al(2)O(3) crystals have been established. On the basis of this, the SH parameters including zero-field splitting parameter D and Zeeman g-factors (g(||) and g(perpendicular)) for Cr(4+) ions in Cr(4+):alpha-Al(2)O(3) crystals, taking into account the spin-spin (SS), spin-other-orbit (SOO) and orbit-orbit (OO) magnetic interactions in addition to the spin-orbit (SO) magnetic interaction, are theoretically investigated using complete diagonalization method (CDM). The theoretical results are in excellent agreement with the experimental ones when the upper three O(2-) ions rotate 0.94 degrees toward [111] axis and the lower three O(2-) ions rotate 0.92 degrees toward it. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Cr(4+) ions in Cr(4+):alpha-Al(2)O(3) crystals. This study shows that for Cr(4+):alpha-Al(2)O(3) the contributions arising from SS, SOO, and OO interactions to the zero-field splitting (ZFS) parameter D are appreciable, whereas those to g(||) and g(perpendicular) are quite small.