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

非破坏性磁体的先前最高磁场为80.3 T，脉冲持续时间为8 msec。记录场由内增强多层线圈更新。新的最高场为80.8 T，持续时间为25 msec。测试磁体的寿命表明，67.5 T的磁场可以产生超过40次发射。用于加强磁体的环的外径（D）被最小化。150 mm的D用于持续时间为7 msec的短脉冲磁体。在70 mm的情况下，磁体在50 T的磁场下被破坏，但90 mm的环在最高场射击后幸存下来。通过对环的测试，确定D为100 mm。小环有一个很大的优点，就是磁体可以快速冷却，例如，我们可以每15分钟产生一个60 T的发射。同轴型磁化拾取线圈（MPC）已安装在稀释冰箱。同轴MPC解决了其他类型MPC中磁场不均匀对信号影响较大的问题，提高了测量精度，将ZYLONTM应用<TM>于高压容器的加固，使高压下的高场磁化测量成为可能。用Cu-Be材料制作的微高压池，可以很容易地获得1GPa的压力，但脉冲场产生的涡流会使温度升高。用ZYLON增强的薄压力容器将提供精确的测量，在极低温度下的高场磁化强度测量已经取得了很大的进展。在样品的磁化曲线中观察到了场致磁有序现象。自旋带隙材料SrCu_2（BO_3）_2的磁化强度测量清楚地显示出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.