研究発表

超伝導は転移温度以下で電気抵抗が 0 になる現象で, 超伝導磁石や送電線に応用されている. 今回扱う鉄系超伝導体 SmFeAsO1-xHx は, SmO 層と FeAs 層が積み重なった構造を取る. 水素負イオンをドープすると生じた電子が鉄の反強磁性相を消し, 55 K 以下で超伝導相になる. 水素負イオンドープは多量の電子を供給でき, 超伝導転移温度を上げることが可能となる利点がある. LaFeAsO由来の超伝導体は転移温度が約 7 K 上昇して 35 K になる. 我々は試料SmFeAsO0.77H0.14の磁気測定により, この試料の臨界電流密度を明らかにした.

鉄系高温超伝導体の内、最も高い超伝導転移温度を示すSmFeAsO1-xFxの低温合成温度の低減には、正方晶を示すSmFeAsOの結晶相出現条件のうち、最も低い温度を明らかにすることは有用である。過去に報告されたうち、最も低温でのSmFeAsO相出現を、電子顕微鏡とエネルギー分散型X線発光分析による解析を用いて明らかにする。

After the discovery of graphene in 2004, 2D magnetic materials have earned a great interest among condensed matter physicists and material engineers due to their fascinating magnetic properties. The 2D magnetic materials have proven that they are worth of investigating as they gave birth to van der Waals materials or topological insulators. They are the type of materials that will introduce the new era for information and semiconductor technology. The previous paper by R. Sakagami et el demonstrated that EuSn2As2 samples were prepared from Eu ingots and Sn-As pallets through a liquid phase reaction in carbon crucibles within vacuum silica tubes.) The resulting crystal structure of EuSn2As2 has a sandwich shape where top and bottom layers are Eu, and SnAs bilayer is positioned in between Eu layers. After successful synthesis, heat capacity measurement was performed through physical property measurement system (PPMS) from Quantum Design Inc. As shown in Figure, we observed that there was a sudden increase of heat capacity around 24 K which implies that antiferromagnetic transition occurred. It is noted that the heat capacity of EuSn2As2 tends to follow Dulong-Petit limit at high temperature which means ultimately it would reach C = 3nR where n is the number of atoms per formula and R is the molar-gas constant. Nevertheless, at sufficiently low temperature, Dulong-Petit law does not hold anymore. It is necessary to take account for lattice vibration which is involving Debye model into our formula to obtain a value of electronic heat capacity, Sommerfeld constant. In the conference, we will demonstrate a Sommerfeld constant for polycrystalline EuSn2As2.