Measurement for Transport and Thermal Properties of Materials with anomalous thermoelectric behaviors at Low Temperatures below 1K

1.建立了表征从室温到0.1K固体性质的热电功率S、热导率κ等物理量的测量系统。2.对低温下具有反常热电性质的材料进行了识别，并从输运和热学性质如电阻率p和比热C等方面对其性质进行了研究。在研究期间，我们在^3He-^4He稀释式制冷器上完成了S和κ，在^3He-^4He制冷机上建立了加压C等系统，并根据这些系统的实验结果研究了几种4f电子化合物的磁性。主要研究结果如下：1.测量了远低于1K的S和Ce(Ni，Pd)_2Ge_2的C，并发现在最低温度范围内，索末菲系数γ与反映非费米液体性质的S/T之间存在着定量的密切关系。报道了价态过渡化合物(Yb&lt；0.8&gt；Y&lt；0.2&gt；)InCu4在2K下的压力感生铁磁相变。在1.2 Gpa的压力下，我们在2K的C中检测到一个锐利的峰，并从熵的角度得到了Yb^&lt；3+&gt；离子在这个相变中冻结了约20%的全矩，认为这个相变是从体相性质出发的，并且是该化合物的本征相变。)Pd_2Si_2在2~300K之间。我们发现，当(La_&lt；0.67&gt；Y_&lt；0.33&gt；)Eu含量超过25%时，合金在20K时的电阻最小，在30K以下的低温下C/T上升较大。我们认为它们可能起源于近藤效应，S对这些合金的测量正在进行中。

Aim for our research is as follows :1.Construction of the measurement systems for thermoelectric power S, thermal conductivity κ and the other physical quantities characterizing properties of solid from the room temperature down to 0.1K.2.Identification of materials with anomalous thermoelectric properties at low temperatures, and research for their nature via transport and thermal quantities such as electrical resistivity p and specific heat C.In the research term, we finished constructing the several systems including S and κ on a ^3He-^4He dilution frigerator, C under pressure using a ^3He-cryostat, and investigated the magnetic properties of several 4f-electron compounds from experimental results obtained using these systems. The main research results are as follows :1.We measured S and C of Ce(Ni,Pd)_2Ge_2 well below 1 K, and detected a quantitative close relation in between the Sommerfeld coefficient γ and the S/T reflecting a non-Fermi liquid nature in the lowest temperature range.2.Mitsuda et al. reported the pressure-induced ferromagnetic transition at 2 K with small magnetic moment in a valence transition compound (Yb_<0.8>Y_<0.2>)InCu_4 by magnetization measurement. We detected a sharp peak at 2 K in C under 1.2 GPa, and obtained about 20 % of the full moment of Yb^<3+> ion is frozen with this phase transition from the entropy consideration, concluding this transition is from a bulk property and intrinsic in this compound.3.We measured p and C of a valence fluctuator EuPd_2Si_2 and its 'isovolume' diluted alloys (Eu(La_<0.67>Y_<0.33>)Pd_2Si_2 between 2 and 300 K. We found both the resistance minimum at 20 K and the C/T upturn reaching large amount at low temperatures below 30 K for the alloys beyond 25 % of substitution of Eu by (La_<0.67>Y_<0.33>). We consider they may originate from the Kondo effect, and the measurements of S for these alloys are in progress.