大坂 藍

A intermediate multidomain state and large crystallographic tilting of 1.78° for the (hh0)pc planes of a (001)pc-oriented single-domain Mn-doped BiFeO3 (BFMO) thin film were found when an electric field was applied along the [110]pc direction. The anomalous crystallographic tilting was caused by ferroelastic domain switching of the 109° domain switching. In addition, ferroelastic domain switching occurred via an intermediate multidomain state. To investigate these switching dynamics under an electric field, we used in situ fluorescent X-ray induced Kossel line pattern measurements with synchrotron radiation. In addition, in situ inverse X-ray fluorescence holography (XFH) experiments revealed that atomic displacement occurred under an applied electric field. We attributed the atomic displacement to crystallographic tilting induced by a converse piezoelectric effect. Our findings provide important insights for the design of piezoelectric and ferroelectric materials and devices.

For high-performance spintronic applications with Co-based Heusler alloys, we explore Si1−xGex(111) grown by liquid phase epitaxy (LPE) with Al–Ge mixed paste, where x is the Ge content. By annealing the screen printed Al–Ge paste on a Si(111) substrate, a continuous Si1−xGex(111) layer with a smooth interface between the Si1−xGex layer and Si substrate is epitaxially grown. The surface with residual paste is polished and treated by chemical mechanical polishing and a catalyst referred etching (CARE) process, resulting in a reduction of the root-mean-square roughness to 0.52 nm over a large-scale area. After the surface treatments of the LPE-Si1−xGex, we can obtain Si0.93Ge0.07(111) to epitaxially grow one of the Co-based Heusler alloys, Co2FeSi. The magnetic properties and intermixing at the Co2FeSi/LPE-Si0.93Ge0.07(111) interface are consistent with those at the Co2FeAl0.5Si0.5/Si(111) and the Co2FeAl0.5Si0.5/Ge(111) interfaces. The Al–Ge-paste-induced LPE-Si1−xGex(111) and the CARE process for the surface are quite effective for the growth of Co-based Heusler alloys in future SiGe-based spintronic devices.