DEVELOPMENT OF METHOD FOR MAGNETIZATION MEASUREMENT IN PULSED HIGH MAGNETIC FIELD COMBINED WITH HIGH PRESSURE AND LOW TEMPERATURES

原来无损磁铁的最高磁场为80.3T，脉冲宽度为8ms。记录的磁场已由内部加固的多层线圈更新。新的最高场强为80.8T，持续时间为25毫秒。对该磁体的寿命测试表明，该磁体可产生超过40次的67.5T磁场，使磁体加固环的外径(D)最小化。短脉冲磁体的直径为150 mm，持续时间为7ms。在70 mm的情况下，磁体在50T的场强下被破坏，但90 mm环在最高场射后存活。通过环件试验，确定D为100 mm。小环具有磁体快速冷却的优点，可以每15分钟产生一次60T的放电。稀释式制冷机中安装了同轴式磁化拾取线圈。采用同轴式磁强计，解决了磁场不均匀对其他类型磁强计信号影响较大的问题，提高了测量精度；将Zylon^&lt；TM&gt；应用于高压室加固，实现了高压下高场磁化强度的测量。通常的高压室是用铜-铍材料制成的，很容易得到1 Gpa的压力，但脉冲电场产生的涡流会使温度升高。由Zylon增强的薄压力盒将提供精确的测量。在极低温度下的强场磁化测量已经显示出很大的进展。在霍尔丹材料NDMAZ的磁化曲线上观察到场感应磁有序现象。自旋能隙材料SRCu2(BO_3)_2的磁化强度测量表明，磁化强度为1/8-，1/4-，1/3-平台。

Former highest magnetic field by non-destructive magnet was 80.3 T with pulse duration of 8 msec. The recorded field has been renewed by multi-layer coil with inner reinforcement. New highest field is 80.8 T with the duration of 25 msec. Testing the life-time of the magnet makes it clear that the field of 67.5 T can be generated more that 40 shots.Outer diameter (D) of the ring for reinforcement of the magnet is minimized. D of 150 mm was used for the short pulse magnet with the duration of 7 msec. In the case of 70 mm, the magnet was destroyed at the field of 50 T but 90 mm-ring survived after highest field-shot. Through the test of the ring, D is decided to be 100 mm. The small ring has a great advantage that the magnet can be cooled down quickly, e.g., we can generate a 60 T shot every 15 minutes.Co-axial type of magnetization-pick-up-coil (MPC) has been installed in the dilution refrigerator. The problem that the inhomogeneous field has much influence on the signal for other type of MPC is solved by the co-axial MPC and the measurement accuracy is improved.Applying ZYLON^<TM> to the reinforcement of high-pressure cell has made it possible to carry out the high field magnetization measurement under high pressure. Usual high-pressure cell is made of Cu-Be and 1 GPa can be obtained easily but eddy current induced by pulsed field increases temperature. Thin pressure cell reinforced by ZYLON will provide precise measurement.The high field magnetization measurement at very low temperatures has shown a great progress. Field induced magnetic ordering was observed in the magnetization curves of the Haldane material NDMAZ. The magnetization measurement in the spin gap material SrCu_2(BO_3)_2 shown the magnetization 1/8-, 1/4-, 1/3-plateaux clearly.