Development of Precise Magnetic Measurements in a Diamond-Anvil Cell

该项目的目标是在SQUID振动线圈磁强计技术的基础上，提高钻石顶压室中高压磁测量的灵敏度和准确性。检测线圈的导线的一部分被设置为自由移动以使检测线圈振动。新设计的夹持移动部分端部的硬件成功地抑制了导线的不规则摆动，使磁测量的信噪比显著提高。采用压配合的方法，利用Stycast#2850GT实现了将金刚石锤紧凑地机械固定到活塞上，以消除由于环氧键合而产生的磁性背景。除了减少背景信号外，结构简单，便于在活塞上装配砧板。研制了一种复合垫片，可用于在金刚石顶压室中高达30 Gpa的压力下进行精确的磁测量。它的设计使得载荷主要由NiCrAl合金制成的内部部分支撑，该内部部分略大于砧座的衬垫，立方体腰带防止它断裂。对于如此制备的垫片，其磁贡献几乎与具有相同尺寸的立方体垫片相同，并且在30 Gp时保证了大于30um的厚度。为了检验所开发的产品的性能，我们对Cs_2CuF_4在不同压力下进行了磁化率测量，测量压力高达26 Gpa，首次在21 Gpa附近发现了压力感生磁相变。我们成功地将测量精度提高了一个数量级，并将压力提高到30 Gpa左右，以实现精确的磁测量。

The goal of the project is to improve the sensitivity and the accuracy of high-pressure magnetic measurements in a diamond anvil cell, based on the technology of the SQUID vibrating coil magnetometer.1. One part of the lead wire of the detection coil is set to move freely for vibration of the detection coil. Newly designed hardware for clamping the end of the moving part is succeeded to suppress an irregular swing of the lead wire, so that the signal-to-noise ratio of the magnetic measurements increases remarkably.2. Using a press-fit method, a compact mechanical fixing of the diamond-anvils to the pistons has been achieved to eliminate the magnetic background due to epoxy bonding using Stycast #2850GT. Besides reducing the background signal, the simple structure makes it easy to assemble anvils on the pistons.3. A composite gasket for precise magnetic measurements at pressures up to around 30 GPa in a diamond-anvil cell has been developed. It was designed so that the load is supported mainly by the inner part made of a NiCrAl alloy, slightly larger than the culets of the anvils, and the CuBe girdle prevents it from fractured. For the gasket thus prepared the magnetic contribution was almost the same as that of a CuBe gasket having the same size, and a thickness of greater than 30 um was assured at 30 GPa.4. In order to test the performance of the products thus developed we have carried out magnetic susceptibility measurements of Cs_2CuF_4 at various pressures up to 26 GPa and found for the first time a pressure induced magnetic phase transition at around 21 GPa.We have succeeded to achieve one order improvement of the accuracy of the measurements as well as an increase of the pressure to around 30 GPa for precise magnetic measurements.