加热环境对人工合成磁赤铁矿热磁行为的影响

Thermomagnetic measurements including high temperature magnetic susceptibility and high temperature magnetization, are the crucial way to distinguish magnetic minerals by determining the turning points (e.g. Curie point, Neel point or other transforming points) on thermomagnetic curves. In this study, two synthetic maghemite samples are subjected to different thermal environments (open, close, close with Ar or N₂, which defined by the air exposure degree) with 4 instruments for thermomagnetic measurements. The results turn out that Curie point and curve reversibility between heating and cooling are significantly affected by the heating environments. The Curie point corresponding to magnetite is lower in closed environment than that of maghemite in open environment. And the degree of curve irreversibility in open environment is much higher than that in closed environment. Redox environments account for the differences above. Because the maghemite in closed environment transforms into magnetite when heated up to 250°C, it is impossible to be distinguished by its curie point; the final mineral in open environment (oxidizing environment) is hematite which can be determined by the Curie point. The results suggest that maghemite likely displays very differently in different heating environments. Therefore single thermomagnetic curve tends to misleading in determining magnetic minerals. Combination of measurements in different conditions is essential to obtain more accurate estimation.