[22p-E205-1~16] 10.1 Emerging materials in spintronics and magnetics (including fabrication and characterization methodologies)

▲ [22p-E205-14] High-quality sputtered BiFeO₃ for ultra-thin epitaxial films

Tomohiro Ichinose¹, Daisuke Miura¹, 〇Hiroshi Naganuma¹ (1.Tohoku Univ.)

Keywords:Multiferroics, Ultra thin film

BiFeO₃ films were grown on SrTiO₃ (001) substrates by RF magnetron sputtering. The optimal sputtering conditions for a slightly excess Bi content produced high-quality parameters: an atomically flat surface, low leakage current, high ferroelectric polarization (72 µC/cm² // [001]_pc), and large exchange bias (~140 Oe). In addition to these typical characterizations, we carried out two advanced analyses: (i) The lattice constant was identified by Bragg’s diffraction specific to a space group of R3c using X-ray diffraction; it was precisely determined as an expanded a-axis and a shrunk c-axis. (ii) The ferroelectricity was analyzed by first-order reversal curve (FORC) diagrams, which revealed that ferroelectric switching was packed in the narrow electric field area; an internal electric field in the film body was not observed despite the fact that the BiFeO₃ films were as-grown samples. A 3-nm-thick BiFeO₃ film with a continuous and flat surface and flat interface was confirmed by STEM observation. The crystal symmetry was identified as a space group of R3c by analyzing nanobeam diffraction patterns. The ferroelectricity was confirmed by the piezoelectric microscopy response owing to low J_c. A 0.4 nm-thick ultra-thin BiFeO₃ film was confirmed to be a continuous one-unit cell perovskite layer.