This paper studied the crystallization process, phase transition and magnetic properties of amorphous iron oxide nanoparticles prepared by the microwave heating technique. Thermal analysis and magnetodynamics studies revealed many interesting aspects of the amorphous iron oxide nanoparticles. The as-prepared sample was amorphous. Crystallization of the maghemite γ-Fe2O3 (with an activation energy of 0.71 eV) and the hematite α-Fe2O3 (with an activation energy of 0.97 eV) phase occurred at around 300 °C and 350 °C, respectively. A transition from the maghemite to the hematite occurred at 500 °C with an activation energy of 1.32 eV. A study of the temperature dependence of magnetization supported the crystallization and the phase transformation. Raman shift at 660 cm−1 and absorption band in the infrared spectra at 690 cm−1 showed the presence of disorder in the hematite phase on the nanoscale which is supposed to be the origin of the ferromagnetic behaviour of that antiferromagnetic phase.

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We have measured polarized Raman spectra of MnWO 4 single crystals at low temperatures, and studied the temperature dependence of the various phonon modes. From our Raman studies of the MnWO 4 , a new transition temperature, ∼180 K, was found. We have completely assigned the symmetries of the 18 observed Raman modes of the MnWO 4 , as expected from a group theoretical analysis. These Raman modes have been classified into three groups according to weak, intermediate and strong temperature dependence of the modes in each group. Six internal modes have been identified by their weak temperature dependence of the Raman wavenumbers. The temperature dependence of the wavenumbers of the B g modes in Mg-O bonds, modes of intermediate temperature dependence group, shows an anomalous behavior under 50 K. The phonon modes of strong temperature dependence show an anomalous change at ∼180 K in the linewidths. This is believed to be a new transition temperature which involves the changes in the inter-WO 6 octahedra structure.

Both polarized and unpolarized Raman scattering studies of seven tourmalines from the Lucyen mines in Vietnam are presented. These tourmalines, according to their chemical compositions, can be classified into four groups: G1, liddicoatite; G2, elbaite; G3, uvite; and G4, feruvite. The Raman spectra were recorded in two spectral ranges, i.e. 150-1600 cm −1 and 3000-4000 cm −1 . In the lower spectral range, which covers the metal ion-oxygen bond vibrations, all the observed A 1 and E modes are identified. In the higher spectral range, we investigated the OH stretching vibrations and showed that all the observed OH stretching modes have the A 1 character. In both spectral ranges, we found that the same group classification of tourmalines can be applied, and the grouping characterizations are consistent with the chemical composition results.