1.Wuhan National High Magnetic Field Center, Huazhong University of Science and Technology, Wuhan 430074, China 2.State Key Laboratory of Advanced Electromagnetic Engineering and Technology, Huazhong University of Science and Technology, Wuhan 430074, China
Fund Project:Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0401703)
Received Date:19 July 2019
Accepted Date:24 August 2019
Available Online:27 November 2019
Published Online:05 December 2019
Abstract:In recent years, measuring the electrical transport properties of materials in different directions of applied magnetic field has become an important experimental study of topological quantum materials. With the development of condensed matter physics, scientific research has shown that under the ultra-high intensity pulsed magnetic field, the electrical transport study of materials may extend to the quantum limit region, and more abundant physical phenomena will be observed. However, in the existing electric transport measurement system, the rotation sample rod under the action of steady-state field presents a large size and significant eddy current effect, which makes it difficult to meet the requirements for pulsed field measurement, and the current commercial physical property measurement system (PPMS) can only operate under ±16 T steady magnetic field. In addition, the conventional rotation sample rod encounters the problems of insufficient angular resolution and space utilization when used in pulsed high magnetic environment. So there is an urgent need to develop a higher performance rotation measurement system. In view of the above background, in this paper we present a kind of electrical transport measurement system designed by Wuhan National High Magnetic Field Center (WHMFC), which consists of five modules: pulse power supply, pulse magnet, control center, cryogenic system, and signal measurement. The key component is the sample measuring rod with rotation function, which restricts the movement of the drawbar through a double-groove structure to achieve an angular change in a range from –5° to 185°. An angle calibration coil is mounted on the back of the sample stage. Based on the double-calibration method, the angle control accuracy of 0.1° is achieved. The temperature, magnetoresistance and Hall resistance signal are collected by the integrated circuit on sample stage and extracted by compensation circuit and virtual digital lock-in amplifier, and the accuracy of electric transport measurement is better than 0.1 mΩ. Furthermore, the effect of eddycurrent and material deformation at low temperatures are completely eliminated by using polyetheretherketone material, which effectively improves the stability and reliability of the rotation sample rod. Using this measuring rod, we complete a series of experiments in the 8 mm sample cavity in the center of the pulse magnet: the minimum ambient temperature reaches 1.3 K, the maximum magnetic field strength arrives at 65 T, and the direction angle of the magnetic field is able to change in a 190° range. Thus the universally applicable measurement system of electric transport experiment in pulsed high magnetic field is successfully established. In this paper, we elaborate the principle and device components of the measurement system, the design and fabrication of the angle measuring rod, and the calibration principle and measurement process. Relevant experimental results show that the system has important application value in the research of 3D Fermi surface, topological insulator surface state, quantum limit transport, superconductivity analysis, etc. Based on this system, the electrical transport experimental system at WHMFC provides an effective means for the relevant research teams (home and abroad) engaged in the exploration of the intrinsic physical characteristics of quantum materials in extremely pulsed high magnetic field and low temperature environment. Keywords:pulsed high magnetic field/ electrical transport measurement/ level rotation sample rod
全文HTML
--> --> --> -->
3.1.拉杆式转角样品杆的结构设计
为了解决以上问题, 设计了一种新型的基于多重拉杆结构的转角样品杆, 其旋转杆内部机械结构如图3(a)所示, 其中, 1是角度控制旋钮, 2是带有螺纹的传导管, 1与2分别作为螺母和螺杆, 共同构成螺栓结构. 转动旋钮螺母时, 带动螺杆2做上下移动; 3是传动杆, 4是水平滑槽, 5是斜滑槽, 4和5同时对3进行限位, 使其仅有一个位移自由度, 保证了运动轨迹的唯一性. 通过交叉滑槽结构控制传动杆, 只需要在样品台背面取一个支撑点6, 即可形成杠杆结构, 实现–5°—185°转角功能. 其转角为0°, 90°, 180°时, 机械结构状态如图3(b)所示. 其中位于样品台背面的7是角度标定线圈, 用于检测样品台的旋转角度, 8是温度计, 即热敏贴片电阻, 用于实验过程中测量样品台的即时温度; 9是样品台正面, 用于搭载样品并固定引线, 一般通过四线法来测量样品的磁阻、霍尔电阻等参数. 这种旋转机构中传动杆下方支点通过样品台背面的转轴孔与样品台连接, 从背面带动样品台旋转, 不占用样品台正面空间, 从而最大限度地保留了样品台面积, 较传统方式有更高的空间利用率, 最小可以在直径7—9 mm的圆柱空间内使用, 在测量准确度和可靠性方面均取得有效提升. 图 3 武汉强磁场中心转角样品杆 (a)机械结构图; (b) 转角示意图; (c) 角度标定原理图 Figure3. Rotation sample rod in WHMFC (Wuhan National High Magnetic Field Center): (a) Mechanical structure diagram; (b) situation at different angles; (c) principle of angle calibration.