High temperature stability of natural maghemite: a magnetic and spectroscopic study

摘要: SUMMARY A combined magneto-mineralogical approach is used to diagnose maghemitization in magnetic grains of basaltic rock fragments from sand dunes the Namibian desert SW Africa. Data were obtained static analysis, ferromagnetic resonance (FMR) spectroscopy, micro-Raman spectroscopy and electron microscopy. Micro-Raman showed that lithic form oxidative solid solution series with magnetite maghemite as end-members. The five active Raman modes at 712, 665, 507, 380 344 cm −1 indicate has well-defined structural properties. FMR spectral analysis provides evidence for long-range dipolar coupling, which suggests intergrowth phases series. Thermomagnetic experiments hysteresis measurements reveal a Curie temperature about 890 K this maghemite. Upon heating 970 part altered thermodynamically more stable hematite. After selective thermal decomposition protected atmosphere, remaining phase 850 K, characteristic magnetite. unique stability natural above its explained by mineral structure, formed during slow alteration under arid climate conditions.