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金刚石压砧单元中高压磁性测量的灵敏度和准确度。检测线圈的引线的一部分被设置为自由移动以用于检测线圈的振动。新设计的运动部件端部夹紧硬件成功地抑制了引线的不规则摆动，从而大大提高了磁测量的信噪比.使用压配合方法，实现了金刚石砧与活塞的紧凑机械固定，以消除由于使用Stycast #2850GT进行环氧树脂粘合而产生的磁背景。除了降低背景信号外，简单的结构使其易于在活塞上组装砧座。研制了一种用于在金刚石压砧室中进行压力高达30 GPa左右的精密磁性测量的复合垫片。它的设计使得负载主要由NiCrAl合金制成的内部部分支撑，略大于砧座的底脚，并且CuBe环带防止其断裂。对于如此制备的垫圈，磁贡献几乎与具有相同尺寸的CuBe垫圈相同，并且在30 GPa下确保大于30 μ m的厚度。为了检验所研制产品的性能，我们对Cs_2CuF_3的磁化率进行了测量。首次发现在21GPa附近存在压力诱导的磁相变，并成功地将测量精度提高了一个数量级，同时将压力提高到30GPa左右，使磁相变的精确测量精度提高了一个数量级。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.