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

我们的研究目标如下：1.研究目标：热电功率S、导热系数κ等表征固体在室温至0.1K.2范围内性质的物理量测量系统的构建。在低温下异常热电性能材料的鉴定，并通过电阻率p和比热C等输运和热量研究其性质。在研究期内，我们在^3He-^4He稀释冰箱上完成了S和κ系统的构建，在^3He-低温恒温器的压力下完成了C系统的构建。并根据实验结果研究了几种4f电子化合物的磁性能。主要研究成果如下：1。我们测量了远低于1k的Ce(Ni,Pd)_2Ge_2的S和C，并在最低温度范围内检测到Sommerfeld系数γ与S/T之间的定量密切关系，反映了非费米液体性质。Mitsuda等人报道了一种价态跃迁化合物（Yb_<0.8>Y_<0.2>）InCu_4在2 K下的小磁矩压力诱导铁磁跃迁。在1.2 GPa的温度下，我们在C的2 K处发现了一个陡峰，从熵的角度考虑，Yb^<3+>离子约有20%的完整力矩被冻结，从而得出这种相变是来自于该化合物的体性质和固有的。我们在2 ~ 300 K范围内测量了价波动子EuPd_2Si_2及其“等体积”稀释合金(Eu(La_<0.67>Y_<0.33>)Pd_2Si_2的p和C。结果表明，在La_<0.67>Y_<0.33>)取代Eu超过25%的合金，在20k时电阻最小，而在30k以下的低温下，C/T上升幅度较大。我们认为它们可能源于近藤效应，这些合金的S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.