Brialmont S, Fagnard J F, Vanderbemden P
SUPRATECS and Department of Electrical Engineering and Computer Science (B28), University of Liège, Sart-Tilman, B-4000, Belgium.
Rev Sci Instrum. 2019 Aug;90(8):085101. doi: 10.1063/1.5111399.
The development of large size magnetic materials requires nondestructive measurement techniques to characterize their magnetic moment. In this work, we report the design and construction of a torque magnetometer able to accommodate sizable magnetic samples (>1 cm) both at room temperature and cryogenic temperature. This device has an intermediate sensitivity between miniature torque magnetometers designed to work at cryogenic temperature and industrial torquemeters poorly adapted to extreme conditions. We show that torque sensing in the range 10-100 Nm can be achieved with piezoresistive metallic strain gages cemented on a cylindrical aluminum shaft with external temperature control. An absolute calibration of the device, carried out with a coil fed by a DC current, shows that magnetic moments down to 5 × 10 A m can be measured by this technique. The magnetometer is used to characterize a Nd-Fe-B permanent magnet and a permanently magnetized bulk, large grain superconductor at liquid nitrogen temperature (77 K). Results are in excellent agreement with data obtained with a flux extraction magnetometer for large samples. The device is able to measure magnetic moments in excess of 1.5 A m, i.e., two orders of magnitude above the maximum magnetic moment of commercial magnetometers. The sample can be inserted in the air-gap of an electromagnet to measure the decrease in magnetic moment in the presence of a transverse applied field. The device was used to characterize the magnetic moment of "quasibulk" superconductors made of stacked coated conductor tapes (12 mm width) in such "crossed field" conditions.
大型磁性材料的研发需要无损测量技术来表征其磁矩。在本工作中，我们报告了一种扭矩磁力计的设计与构建，该磁力计能够在室温及低温下容纳尺寸较大的磁性样品（>1 cm）。此装置的灵敏度介于设计用于低温工作的微型扭矩磁力计和不太适用于极端条件的工业扭矩计之间。我们表明，通过将压阻式金属应变片粘贴在带有外部温度控制的圆柱形铝轴上，可实现10 - 100 Nm范围内的扭矩传感。通过由直流电流供电的线圈对该装置进行的绝对校准表明，利用此技术可测量低至5×10 A·m的磁矩。该磁力计用于表征钕铁硼永磁体以及液氮温度（77 K）下的永久磁化块状大晶粒超导体。结果与使用磁通提取磁力计对大尺寸样品测得的数据高度吻合。该装置能够测量超过1.5 A·m的磁矩，即比商用磁力计的最大磁矩高出两个数量级。样品可插入电磁铁的气隙中，以测量在横向施加磁场时磁矩的减小。该装置用于在这种“交叉场”条件下表征由堆叠的涂层导体带（宽度12 mm）制成的“准块状”超导体的磁矩。
