We have investigated the polarization dependence of the near-band-edge photoluminescence and photoreflectance spectra in nonpolar (A-plane) ZnO films under strong biaxial compressive strain. We show that anisotropic strain and the orientation of the nonpolar plane play an important role in determining the polarization selectivity and properties of excitonic transitions. We identified four distinct band-edge transitions at 3.449, 3.420, 3.386, and 3.326eV. They were identified as E2 and E1 free excitons, E1 excitons bound to a donor, and free-electron-to-bound-hole transition, respectively. Unlike previously reported results on relatively thick nonpolar films, the E1 exciton (lowest energy) was mainly polarized to E⊥c and weakly polarized to E∥c under strong biaxial compressive strain in the 100nm thick film. The E2 exciton (next higher energy) was exclusively polarized to E∥c. The localization energy of DX is 34meV, which is much larger than that in polar ZnO, and the DX was not thermally delocalized even at room temperature.

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CuFe 2 O 4 has been studied by Mo È ssbauer spectroscopy and X-ray diffraction. The crystal is found to have a tetragonal spinel structure with the lattice constants a 0 (5.805 AE 0.005) # e and c 0 (8.669 AE 0.005) # e. The iron ions are in ferric Fe 3 states. The temperature dependence of the magnetic hyperfine fields at 57 Fe nuclei at the tetrahedral (A) and octahedral (B) sites is analyzed by the Ne  el theory of ferrimagnetism. The intersublattice superexchange interaction is found to be antiferromagnetic with its strength of J AÀB À19X5k B while intrasublattice superexchange interactions are ferromagnetic with their strengths of J AÀA 3X1k B and J BÀB 4X4k B .

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