Local structure distortion and spin Hamiltonian parameters of oxide-diluted magnetic semiconductor Mn-doped ZnO

The local structure distortion, the spin Hamiltonian (SH) parameters, and the electric fine structure of the ground state for Mn^2+(3d^5) ion in ZnO crystals are systematically investigated, where spin--spin (SS), spin--other--orbit (SOO) and orbit--orbit (OO) magnetic interactions, besides the well-known spin--orbit (SO) coupling, are taken into account for the first time, by using the complete diagonalization method. The theoretical results of the second-order zero-field splitting (ZFS) parameter D, the fourth-order ZFS parameter (a-F), the Zeeman g-factors: g_// and g_\bot, and the energy differences of the ground state: \delta_1 and \delta_2 for Mn^2+ in Mn^2+: ZnO are in good agreement with experimental measurements when the three O^2- ions below the Mn^2+ ion rotate by 1.085^\circ away from the 111-axis. Hence, the local structure distortion effect plays an important role in explaining the spectroscopic properties of Mn^2+ ions in Mn^2+: ZnO crystals. It is found for Mn^2+ ions in Mn^2+: ZnO crystals that although the SO mechanism is the most important one, the contributions to the SH parameters, made by other four mechanisms, i.e. SS, SOO, OO, and SO\simSS\simSOO\simOO mechanisms, are significant and should not be omitted, especially for calculating ZFS parameter D.