| Budget Amount *help |
¥3,820,000 (Direct Cost: ¥3,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2007: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
Fiscal Year 2006: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Research Abstract |
Spin glass behavior of ternary uranium compounds with composition 2:1:3 are investigated under high pressure in this work. We have systematically measured the magnetic properties of U_2PdSi_3 and U_2AuGa_3 (chosen as the typical samples of 2:1:3 uranium compounds) and AuFe (8 at. %Fe) (chosen as a reference sample) under high pressure including the temperature dependences of ac and dc susceptibility, magnetization and magnetic relaxation. The obtained results are summarized as following. (1) A1B_2-type compound U_2PdSi_3: Measurements were carried out on a single crystalline sample within the c-plan. It is observed that the spin glass transition temperature T_f decreases monotonously with increasing the pressure, while the frequency change rate dT_f (=ΔT_f/(T_fΔlogω)) of T_f increases linearly with increasing the pressure up to 1 Gpa. A kinetic analysis reveals that, as pressure increases, the static spin freezing temperature Ts decreases, while critical exponent zv and average excitat
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ion energy E_a/k_B increase monotonously. (2) CeCu_2-type compound U_2AuGa_3: Under high ressure, the U_2AuGa_3 sample shows more complex magnetic behavior than that observed for U_2PdSi_3, it is observed that the spin glass transition temperature T_fU_2AuGa_3 increases with pressure up to 1 Gpa, but its frequency change rate δT_f increasing with pressure up to 0.5 Gpa, then the δT_f value monotonously falls with an increase in pressure. Fitting the T_f (ω) data to the critical slowing down and Vogel-Fulcher law, it is obtained that critical exponent zv and average excitation energy E_a/k_B increase firstly with pressure, reaching their respective maximum value near 0.5 Gpa, and then decrease with increasing the pressure. (3) Reference sampls AuFe (8 at.%Fe): As pressure increases, the spin glass transition temperature Tf increases linearly, while δT_f, zv and E_a/k_B decrease monotonously up to 1 Gpa. In conclusion, we have observed the evident change of NMAD spin glass behavior under high pressure, which could be understood based on the magnetic cluster model. According to this model, magnetic cluster in U_2PdSi_3 and U_2AuGa_3 could exist with different geometric size depending on the degree of randomness and/or relatively strength of magnetic interaction, which could be changed under high pressure. Because the pressure effect of NMAD spin glass behavior in U_2PdSi_3 and U_2AuGa_3 show different feature, it is clear that the geometric size of the clusters and exchange strength between the clusters would change with pressure in different ways for U_2PdSi_3 and U_2AuGa_3. Less
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