Pressure-Induced Magnetic Phase of 4f Hole Systems with a Geometrical Frustration

这项研究的目的是研究重费米子化合物YbAgGe和YbRhSb的压力感生磁相的起源，这种磁相不能被Kondo效应和RKKY相互作用之间的竞争所理解。在YbAgGe的情况下，Yb离子在六方晶面上形成了一个准kagome晶格。该化合物在T_&lt；M_1&gt；=0.8K(二级)和T_&lt；M_2&gt；=0.65K(一级)处发生两次磁相变。对于P&GT；1.6 GPA，T_M突然增加。为了研究YbAgGe的压致相变的起源，用我们用Bridgman顶压室研制的交流量热计进行了高达3 Gpa的比热测量。当P=0.29 GPa时，C(T)在T_t；M_2&gt；=0.75K处的尖点变成了当P=1.15 Gpa时，C的大而尖锐的峰。对于P&GT；2 GPA，在不含Ge…的化合物中观察到的C(T)在T_&lt；M3&gt；处的明显跳跃是二级磁相变的特征行为更令人沮丧的是。由比热数据估算的磁熵T_m、S_m(T_M)大于1.6 Gpa。对于T&gT；T_m，S_m的压力无关性表明，对于P&gt；1.6 Gpa，S_m(T_M)和T_m随压力的增加归因于磁受挫的部分释放，而不是近藤温度随压力的降低。具有ω-TiNiSi型结构的YbRhSb在常压下发生了T_M=2.7K的反常磁化转变，其自发磁矩仅为3×10~(-3)μ_B/Yb。压力下的电阻率测量表明，在Pc=1.6 Gpa时，T_M(P)有一个明显的极小值1.8K。为了研究1.6 Gpa以上的基态的压力诱导相变，进行了交流磁化率、直流磁化强度和比热的测量。随着气压的增加，M值增大，在B_M=3.2T，P=0时观测到的类超磁异常变得更加明显，并向低场移动。在约2 GPa时，B_M(P)外推到B_M=0。在2 Gpa以上，具有变磁行为的反铁磁相转变为铁磁性相。较少

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 … More 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