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

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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.