Destruction of spin cycloid in (111)_c-oriented BiFeO_3 thin films by epitiaxial constraint: Enhanced polarization and release of latent magnetization

摘要

In BiFeO_3 films, it has been found that epitaxial constraint results in the destruction of a space modulated spin structure. For (111)_c films, relative to corresponding bulk crystals, it is shown (ⅰ) that the induced magnetization is enhanced at low applied fields; (ⅱ) that the polarization is dramatically enhanced; whereas, (ⅲ) the lattice structure for (111)_c films and crystals is nearly identical. Our results evidence that eptiaxial constraint induces a transition between cycloidal and homogeneous antiferromagnetic spin states, releasing a latent antiferromagnetic component locked within the cycloid.