The magnetic properties of antiferromagnetic (AFM) spins were investigated using x-ray magnetic linear dichroism (XMLD) in epitaxial NiO/CoO/MgO(001) films as a function of film thickness, temperature, and interface modulation. We found that the NiO AFM spins undergo a spin reorientation transition (SRT) from the in-plane orientation to the out-of-plane orientation at a critical NiO thickness. The NiO AFM SRT can be attributed to the competition between the out-of-plane anisotropy of the NiO AFM spins and the AFM interfacial exchange coupling with the CoO in-plane spins. The NiO SRT thickness increases with the CoO thickness and also with the interfacial coupling strength. The temperature-dependent XMLD measurement indicates that the exchange coupling at the NiO/CoO interface can greatly enhance the Néel temperature of the CoO layer

Single-crystalline silicon, amorphous quartz, and single-crystalline sapphire were used as the substrates for the deposition of nanocrystalline zinc oxide (nc-ZnO) thin films by plasma assisted pulsed laser deposition from metallic zinc at low temperature below 80 °C, and a postdeposition annealing process was performed for the deposited nc-ZnO thin films. The influences of substrate and annealing on the structural and optical properties as well as the photoluminescence of the prepared nc-ZnO thin films were studied. Raman spectroscopy and Fourier-transform infrared spectroscopy measurements reveal the wurtzite ZnO phase in the films. X-ray diffraction results indicate the nanocrystalline structure of the films with c axis perpendicular to substrates. Optical characterization shows that the prepared films have an ultraviolet (UV) absorption edge near 380 nm with a direct band gap of about 3.25 eV. The prepared films emit predominantly UV photoluminescence at light excitation. The structure and properties of the films are dependent on substrates and the annealing process has different influences for the films deposited on different substrates.

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The effect of CoO spin orientation on exchange coupling was investigated in single-crystalline Fe/CoO/MnO/MgO(001) systems. An antiferromagnetic CoO spin reorientation transition from the in-plane direction to the out-of-plane direction was found to be associated with the in-plane strain transition in CoO film from compression to expansion. The induced uniaxial anisotropies by exchange coupling at the Fe/CoO interface are significantly stronger for the in-plane CoO spin orientation than for the out-of-plane CoO spin orientation. Our study provides a way to modify the exchange coupling in the ferromagnetic (FM)/antiferromagnetic (AFM) bilayer by modulating the strain in the AFM film