[21p-S223-1~17] 13.2 Exploratory Materials, Physical Properties, Devices

[21p-S223-16] Coherent interface structure and electronic and magnetic properties of MgO/Mg₂Si/MgB₂ nanocomposites

Katsuya Ueno¹, Yukihito Nagashima², Yusuke Seto¹, Megumi Matsumoto¹, Takahiro Sakurai¹, Hithoshi Ohta¹, 〇Takashi Uchino¹ (1.Kobe Univ., 2.Nippon Sheet Glass)

Keywords:nanocomposite,interface

In this work, we propose a method to synthesize fully dense nanocomposites using solid phase reaction between metallic magnesium and bulk borosilicate glass. We find that a nearly 100 % dense nanocomposite consisting of MgO (insulator), Mg₂Si (semiconductor), and MgB₂ (superconductor) is obtained without performing post-sintering heat treatments. Also, the reactions lead to a self-grown periodic layered structure consisting of alternating MgO- and MgSi₂-rich layers. We further reveal that atomically coherent interfaces are formed at the boundary of the MgO- and MgSi₂-rich layers. The resulting composite shows a rather low resistivity of ~a few Wcm at room temperature although it comprises more than 40 vol% of MgO. Moreover, the nanocomposite shows a semiconductor-superconducting transition at 36 K irrespective of a small volume fraction (~8 vol%) of MgB₂ in the composite. Resistive and magnetic measurements demonstrate that the superconducting transition proceeds in two stages, namely, the intragrain transition at 36 K due to the embedded MgB₂ nanograins and the intergrain transition at ~26 K induced by the Josephson coupled network over the whole of the MgO/Mg₂Si/MgB₂ nanostructures. Thus, the present approach can pave the way towards the creation of high-quality MgO/Mg₂Si/MgB₂ interfaces and the related strong Josephson junctions consisting of physically remote but electrically connected MgB₂ nanograins.