Ferrimagnets having low RF loss are used in passive microwave components such as isolators, circulators, phase shifters, and miniature antennas operating in a wide range of frequencies (1-100 GHz) and as magnetic recording media owing to their novel physical properties. Frequency tuning of these components has so far been obtained by external magnetic fields provided by a permanent magnet or by passing current through coils. However, for high frequency operation the permanent part of magnetic bias should be as high as possible, which requires large permanent magnets resulting in relatively large size and high cost microwave passive components. A promising approach to circumvent this problem is to use hexaferrites, such as BaFe 12 O 19 and SrFe 12 O 19 , which have high effective internal magnetic anisotropy that also contributes to the permanent bias.Such a self-biased material remains magnetized even after removing the external applied magnetic field, and thus, may not even require an external permanent i

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The temperature dependence of phonons in ZnO has been studied using resonance Raman and photoluminescence (PL) emission measurements. Excitation with wavelength 363.8 nm (photon energy 3.409 eV) is used to establish incoming resonance near room temperature. Broad PL emission is seen at room temperature with peak position at 3.25 eV. This coincides with the overtone of the longitudinal optic (LO) band. Up to six LO phonon orders are observed. Temperature dependence of the LO phonon energy is described by a two-phonon decay mechanism with energies 100 and 496 cm−1. The temperature dependence of the PL shift is interpreted based on electron-phonon interactions. A two-phonon description is sufficient to describe the temperature shift in the band gap through occupation at average acoustic and optic phonon energies 125 and 500 cm−1, respectively. LO phonon sidebands (PSBs) are also observed at low temperature (23 to 100 K). The temperature shift in the PSB energies is interpreted based on the band gap shift combined with established theory for the PSBs.

Electrical properties of n-ZnO/n-GaN isotype heterostructures prepared by rf-sputtering of ZnO films on GaN layers which in turn grown by metal-organic vapour phase epitaxy are discussed. Current-voltage (I-V) characteristics of the nZnO/n-GaN diodes exhibited highly rectifying characteristics with forward and reverse currents being ~1.43×10 -2 A/cm 2 and ~2.4×10 -4 A/cm 2 , respectively, at ±5 V. From the Arrhenius plot built representing the temperature dependent current-voltage characteristics (I-V-T) an activation energy 0.125 eV was derived for the reverse bias leakage current path, and 0.62 eV for the band offset from forward bias measurements. From electron-beam induced current measurements and depending on excitation conditions the minority carrier diffusion length in ZnO was estimated in the range 0.125-0.175 µm,. The temperature dependent EBIC measurements yielded an activation energy of 0.462 ± 0.073 V.