反応性高周波スパッタ法によるＦｅ‐Ｂ‐Ｏ系薄膜の作製とその物性

Abstract

Fe-B-Osystem thin films were fabricated by reactive rf sputtering from the composite targets of thin iron sheet and B2O3 tablets. The films are amber in color and have a high transmittance in the visible and the near infrared regions. Unfortunately, the exact identification of crystallographic structure of the films has not yet been succeeded. But judging from diffraction measurement, infrared absorption spectrum and SEM observation, the crystallographic structure of our samples seems to be close to polycrystalline ferric borate, FeBO3, whose c-axis is aligned perpendicular to the film plane. Saturation magnetization (4πMs=44G) is about one half of those reported for FeBO3 single crystal. Surprising-ly, our samples exhibit ferroelectricity at room temperature, despite FeBO3 by no means exhibits ferroelectricity. Saturation spontaneous polarization at room temperature (Ps=0.57μC/cm2) is more than twice that of Rochelle salt. Further we found that humidity plays an essential role for appearance of ferroelectricity. It is suggested that a hydrate formed by penetration of moisture into the films gives rise to ferroelectricity, since some zeolitic hydrates such as FeBO3·nH2O are known in ferric borates.