180掳 Ferroelectric Stripe Nanodomains in BiFeO3 Thin Films

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• 作者：Zuhuang Chen ; Jian Liu ; Yajun Qi ; Deyang Chen ; Shang-Lin Hsu ; Anoop R. Damodaran ; Xiaoqing He ; Alpha T. N鈥橠iaye ; Angus Rockett ; Lane W. Martin
• 刊名：Nano Letters
• 出版年：2015
• 出版时间：October 14, 2015
• 年：2015
• 卷：15
• 期：10
• 页码：6506-6513
• 全文大小：529K
• ISSN：1530-6992

文摘

There is growing evidence that domain walls in ferroics can possess emergent properties that are absent in the bulk. For example, 180掳 ferroelectric domain walls in the ferroelectric-antiferromagnetic BiFeO₃ are particularly interesting because they have been predicted to possess a range of intriguing behaviors, including electronic conduction and enhanced magnetization. To date, however, ordered arrays of such domain structures have not been reported. Here, we report the observation of 180掳 stripe nanodomains in (110)-oriented BiFeO₃ thin films grown on orthorhombic GdScO₃ (010)_O substrates and their impact on exchange coupling to metallic ferromagnets. Nanoscale ferroelectric 180掳 stripe domains with {112虆} domain walls were observed in films <32 nm thick. With increasing film thickness, we observed a domain structure crossover from the depolarization field-driven 180掳 stripe nanodomains to 71掳 ferroelastic domains determined by the elastic energy. These 180掳 domain walls (which are typically cylindrical or meandering in nature due to a lack of strong anisotropy associated with the energy of such walls) are found to be highly ordered. Additional studies of Co_0.9Fe_0.1/BiFeO₃ heterostructures reveal exchange bias and exchange enhancement in heterostructures based on BiFeO₃ with 180掳 domain walls and an absence of exchange bias in heterostructures based on BiFeO₃ with 71掳 domain walls; suggesting that the 180掳 domain walls could be the possible source for pinned uncompensated spins that give rise to exchange bias. This is further confirmed by X-ray circular magnetic dichroism studies, which demonstrate that films with predominantly 180掳 domain walls have larger magnetization than those with primarily 71掳 domain walls. Our results could be useful to extract the structure of domain walls and to explore domain wall functionalities in BiFeO₃.