| Budget Amount *help |
¥3,400,000 (Direct Cost: ¥3,400,000)
Fiscal Year 2006: ¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 2005: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
The purpose of this study is to investigate the origin of a pressure -induced magnetic phase of heavy-fermion compounds, YbAgGe and YbRhSb, which can not be understood by a competition between Kondo effect and RKKY interaction.
1. In the case of YbAgGe, the Yb ions form a quasikagome lattice in the hexagonal c plane of the ZrNiAl-type structure. This compound undergoes two magnetic phase transitions at T_<M1> = 0.8 K (second order) and T_<M2> = 0.65 K (first order). For P > 1.6 GPa, the T_M increases abruptly. In order to examine the origin of the pressure-induced phase transition of YbAgGe, specific heat measurements have been performed up to 3 GPa by an ac calorimeter which we have developed using a Bridgman anvil cell. A cusp of C(T) at T_<M2> = 0.75 K for P = 0.29 GPa changes to the large and sharp peak of C at T_<M2> for P = 1.15 GPa. For P > 2 GPa, a distinct jump of C(T) at T_<M3> is a characteristic behavior for a second-order magnetic transition observed in compounds without ge
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ometrical frustration. The magnetic entropy at T_m, S_m(T_m), estimated by the specific heat data increases above 1.6 GPa. The pressure-independence of S_m, for T > T_m, suggests that the increase of S_m(T_m) and Tm with pressure for P > 1.6 GPa is attributed to a partial release of the magnetic frustration, not decrease of the Kondo temperature with pressure.
2. YbRhSb with an orthorhombic ω-TiNiSi type structure undergoes at ambient pressure a transition into an unusual magnetic state at T_M = 2.7 K, which is associated with very small spontaneous moment of 3 x 10^<-3> μ_B/Yb. The resistivity measurement under pressure revealed that T_M(P) has a pronounced minimum of 1.8 K at P_c = 1.6 GPa.^<5)> In order to investigate the pressure induced transition of the ground state above 1.6 GPa, ac magnetic susceptibility and DC magnetization and specific heat measurements have been carried out up to 3GPa. With increasing pressure, the value of M increases, and the metamagnetic like anomaly observed at B_M = 3.2 T for P = 0 becomes clearer and shifts to low fields. The extrapolation of B_M(P) goes to B_M = 0 at about 2 GPa. Above 2 GPa, the antiferromagnetic phase with metamagnetic behavior changes to a ferromagnetic phase. Less
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