标题： 铁磁性BiFeO$_3$薄膜中从磁力显微镜观察到的150 K以下自旋重取向转变的证据 显示英文标题

标题： Evidence of spin reorientation transition below 150 K from magnetic force microscopy in a ferromagnetic BiFeO$_3$ thin film

摘要： 我们研究了BiFeO$_3$在低温(5-300 K)下的磁性转变，并观察到通过垂直磁力显微镜成像的磁畴几乎90$^o$旋转，在厚度为$\sim$36 nm 的外延薄膜中在150 K范围内。这提供了自旋重取向转变的明确证据。这也证实了在零场冷却和场冷却的磁化率与温度数据中低于$\sim$150 K 的转变。另一方面，室温下的180$^o$域切换表明铁磁性的存在。由于体相反铁磁性的BiFeO$_3$不表现出这样的转变，因此在BiFeO$_3$铁磁薄膜中的这一观察结果表明由于外延应变产生了显著的影响。 基于密度泛函理论的第一性原理计算也揭示了平面内和面外的外延应变共同作用会导致BiFeO$_3$中从G型到C型结构的磁性转变。 显示英文摘要

摘要： We investigated the magnetic transitions in BiFeO$_3$ at low temperature (5-300 K) and observed nearly 90$^o$ rotation of magnetic domains (imaged by vertical magnetic force microscopy) across 150 K in an epitaxial thin film of thickness $\sim$36 nm. It offers a clear evidence of spin reorientation transition. It also corroborates the transition observed below $\sim$150 K in the zero-field-cooled and field-cooled magnetization versus temperature data. The field-driven 180$^o$ domain switching at room temperature, on the other hand, signifies presence of ferromagnetism. Since bulk antiferromagnetic BiFeO$_3$ does not exhibit such a transition, this observation in ferromagnetic thin film of BiFeO$_3$ indicates a radical effect because of epitaxial strain. Density functional theory based first-principles calculations too reveal that combined in- and out-of-plane epitaxial strain induces magnetic transition from G- to C-type structure in BiFeO$_3$.