Sone Keita, Naganuma Hiroshi, Ito Masaki, Miyazaki Takamichi, Nakajima Takashi, Okamura Soichiro
Department of Applied Physics, Faculty of Science, Tokyo University of Science, 6-1-3 Niijuku, Katsushika, Tokyo 125-8585, Japan.
Department of Applied Physics, Tohoku University, 6-6-05 Aoba, Aramaki, Aoba, Sendai 980-8579, Japan.
Sci Rep. 2015 Apr 23;5:9348. doi: 10.1038/srep09348.
A (001)-epitaxial-BiFeO3/CoFe2O4 bilayer was grown by self-assembly on SrTiO3 (100) substrates by just coating a mixture precursor solution. The thickness ratio of the bilayer could be controlled by adjusting the composition ratio. For example, a BiFeOx:CoFe2Ox = 4:1 (namely Bi4CoFe6Ox) mixture solution could make a total thickness of 110 nm divided into 85-nm-thick BiFeO3 and 25-nm-thick CoFe2O4. Self-assembly of the bilayer occurred because the perovskite BiFeO3 better matched the lattice constant (misfit approximately 1%) and crystal symmetry of the perovskite SrTiO3 than the spinel CoFe2O4 (misfit approximately 7%). The magnetic domains of the hard magnet CoFe2O4 were switched by the polarization change of BiFeO3 due to an applied vertical voltage, and the switched magnetic domain size was approximately 100 nm in diameter. These results suggest that self-assembled BiFeO3/CoFe2O4 bilayers are interesting in voltage driven nonvolatile memory with a low manufacturing cost.
通过简单地涂覆混合前驱体溶液，在SrTiO₃(100)衬底上通过自组装生长出(001) - 外延BiFeO₃/CoFe₂O₄双层膜。双层膜的厚度比可以通过调整组成比来控制。例如，BiFeOx:CoFe₂Ox = 4:1（即Bi₄CoFe₆Ox）的混合溶液可以使总厚度为110nm，其中BiFeO₃厚85nm，CoFe₂O₄厚25nm。双层膜的自组装发生是因为钙钛矿BiFeO₃比尖晶石CoFe₂O₄（失配约7%）与钙钛矿SrTiO₃的晶格常数（失配约1%）和晶体对称性更好地匹配。由于施加垂直电压导致BiFeO₃极化变化，硬磁体CoFe₂O₄的磁畴被切换了，并且切换后的磁畴尺寸直径约为100nm。这些结果表明，自组装的BiFeO₃/CoFe₂O₄双层膜在具有低制造成本的电压驱动非易失性存储器方面很有吸引力。
