| Budget Amount *help |
¥3,000,000 (Direct Cost: ¥3,000,000)
Fiscal Year 2003: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 2002: ¥2,500,000 (Direct Cost: ¥2,500,000)
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| Research Abstract |
UGe_2 shows ferromagnetism and superconductivity simultaneously under high pressure and at low temperatures. The ferromagnetic nature had believed to be normal such as Fe, Co and Ni before our present research. The most important fruit in our present work is that ferromagnetic nature of UGe_2 is extremely unusual even at ambient pressure. We have also clarified that the unusual behavior is related to the appearance of superconductivity.
The unusual behavior, which we have discovered, is that magnetization jump appears in the ferromagnetic hysteresis curve only below about 1 K. The essential features of the magnetization jump are as follows : (1)the jump occurs at a definite field, i.e., coercive field Hc. (2)Hc increases with decreasing temperature above 1 K, while Hc flattens below about 1 K. (3)Hc is independent of field sweeping rate. These results strongly suggest that the magnetization jump is attributed to macroscopic quantum tunneling.
We have examined the relation between the jump and the appearance of the superconductivity. There are two characteristic pressures in UGe_2,i.e., Pc〜l6 kbar and Px〜12 kbar. The ferromagnetism disappears at Pc and an unknown phase transition disappears at Px. The superconducting transition has optimum temperature at around Px, suggesting the important role for superconductivity is the unknown phase transition. We found that the jump only appears below Px, indicating the jump is closely related to the unknown phase transition. These results suggest the jump has an influence on superconductivity.
In order to perform these experiments, we developed new static magnetization measurement method. In particular, 'Hall magnetometer' enables us to measure static magnetization very easily at temperatures below 1 K and in pressures up to 10 kbar.
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