Abstract BiFeO3 (BFO), a room-temperature antiferromagnetic-ferroelectric multiferroic, is widely researched due to its potential applications for electric-field control of the magnetism. In this work, the strain control of the phase transition and magnetic properties in the BFO/LaAlO3 heterostructures were investigated. The O K edge polarization-dependent X-ray absorption spectroscopy (XAS) spectra show that the Fe 3d level splits into five levels, which proves that the FeO5 pyramid is asymmetric in the highly strained tetragonal-like BFO. The spin canting induced by the asymmetric structure leads to the magnetic moment. Thus, an obvious magnetic signal in the 17-nm-thick BFO thin films was observed by the Quantum Design magnetic property measurement system. With the increase of the BFO film thickness, the clamping effect induced by the substrate becomes weak, further leading to the BFO phase transition. The O K edge polarization-dependent XAS spectra demonstrate that the orbital reconstruction exists at the mixed BFO phase boundaries. Since the orbital reconstructions can induce the strong magnetic coupling, the magnetic order of the different BFO phases will be coupled with each other. It causes a variation of the magnetic property at the phase boundaries or in the BFO phases.

中文翻译：

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多铁性 BiFeO3 薄膜中相变和磁性的应变控制

摘要 BiFeO3 (BFO) 是一种室温反铁磁-铁电多铁性材料，由于其在磁场控制方面的潜在应用而被广泛研究。在这项工作中，研究了 BFO/LaAlO3 异质结构中相变和磁性能的应变控制。OK 边缘偏振相关 X 射线吸收光谱 (XAS) 光谱显示 Fe 3d 能级分裂为五个能级，这证明 FeO5 金字塔在高度应变的四方 BFO 中是不对称的。由不对称结构引起的自旋倾斜导致磁矩。因此，Quantum Design 磁性能测量系统在 17 nm 厚的 BFO 薄膜中观察到明显的磁信号。随着 BFO 膜厚的增加，由衬底引起的夹持效应变弱，进一步导致 BFO 相变。OK 边缘偏振相关 XAS 光谱表明轨道重建存在于混合 BFO 相边界处。由于轨道重建可以引起强磁耦合，因此不同 BFO 相位的磁序将相互耦合。它会导致相边界处或 BFO 相中的磁性发生变化。