Measurements of magnetic properties of natural rock-forming minerals under pressure

我们的目标是进行一个实验室实验，测量交流（AC）磁化率和它的温度依赖性下的压力约1 GPa。为此，我们开发了一种小型C。长70 mm，由测量互感的初级线圈和次级线圈、加热线圈和热电偶组成，所有这些都是用耐热水泥模制的。然后，线圈系统被放置在实验室制造的活塞缸内，该活塞缸可以通过方便的单轴压力机产生静水压力。我们已经进行了一系列的实验来表征线圈系统在大气压下的磁行为。我们已经使用镍作为测试样品，并成功地测量了磁化率随温度的变化，从而检测到铁磁相变，其Tc相当于镍（631K）的Tc。然后，我们测量了含有纯磁铁矿作为唯一磁性载体的天然火山岩的碎片。我们可以检测到磁铁矿的Tc（853 K）。这些结果表明，新的线圈系统将是有用的，不仅用于检测Tc，但也调查的交流磁化率随频率的变化。后者可为天然岩石中磁性矿物的粒度估计和鉴别提供一种新的手段。最后，我们使用镍通过在c下加压进行了一系列实验。10 MPa.结果似乎是成功的，再现了镍的Tc，但也表明仍然很难精确测量压力下的交流磁化率。需要指出的是，压力变送器应采用固体介质，而不是BN粉末，以避免因BN的体积随压力的增大而发生较大变化，从而导致线圈系统的损坏。

We have aimed to conduct a laboratory experiment for measuring alternating-current (AC) magnetic susceptibility and its temperature dependence under pressure around one GPa. For this purpose, we have developed a small, c. 70mm long, devise that consists of primary and secondary coils for measuring mutual inductance, a heater coil and a thermocouple, all of which are molded with heat-resistive cement. Then, the coil system is placed within a laboratory-made piston cylinder that can give rise to hydrostatic pressure by means of a handy, uni-axial press. We have carried out a series of experiments for characterizing magnetic behaviors of the coil system at an atmospheric pressure. We have used Nickel as a test sample and succeeded in measuring magnetic susceptibility change with temperature, whereby detecting a ferromagnetic phase transition with Tc equivalent to that of Nickel (631K). Then, we have measured fragments of a natural volcanic rock that contains pure magnetite as a sole magnetic carrier. We could detect Tc of magnetite (853K). These results show that the new coil system would be useful for not only detecting Tc, but also investigating changes in AC magnetic susceptibility with frequency. The latter could provide a new means for estimating grain size as well as identifying magnetic minerals in natural rocks. We finally carried out a series of experiments using Nickel by pressurizing at c. 10 MPa. The results appear to be successful, reproducing Tc of Nickel, but also show it still hard to make precise measurements of AC susceptibility under pressure. We should point out that a solid media should be used as a pressure transmitter, instead of BN powder used in this study, in order to avoid break-down of the coil system caused by the greater volume change of BN with the more pressurized.