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Novel Strategy to Create 2D Magnetic Order

Scientists identify the atomic arrangement of an SrRuO3 grain boundary for the first time using advanced imaging, microscopic and spectroscopic techniques.

Defects exist ubiquitously in crystal materials, such as grain boundaries, which are interfaces between two grains (or crystallites) in a polycrystalline material. The properties of grain boundaries strongly depend on their geometry, charge segregation and strain conditions.

Therefore, determining the atomic structure of grain boundaries and revealing the structure-property relations are vital for grain boundary engineering to improve materials and design devices with novel functions. However, experimentally revealing such structure-property relations is very challenging due to the atomic size and chemical complexity of defects, especially for perovskite oxides that contain multiple elements, such as SrRuO3.

SrRuO3 is widely used as electrodes for the growth of thin films, such as superconductors and ferroelectrics. The microstructure of the grain boundaries in SrRuO3 may propagate into the thin films, and thus the defect properties can significantly influence the device properties. However, the atomic structure of grain boundaries in SrRuO3 has rarely been studied, and the effects of their presence on thin film devices are largely unknown.

In a new research article published in the Beijing-based National Science Review, scientists across universities and institutions in China collaborated to determine the atomic structure (including oxygen positions) of an SrRuO3 grain boundary using the recently developed atomically resolved integrated differential phase contrast (iDPC) imaging technique and atomically resolved energy dispersive X-ray spectroscopy (EDS) with aberration corrected advanced scanning transmission electron microscopy (STEM).

Based on the obtained atomic structure, they performed density functional theory (DFT) calculations and found that along the grain boundary, the magnetic moments were reduced by approximately 91 percent on one side and approximately 25 percent on the other side. They discovered that owing to the Ru-O octahedron distortion near the asymmetric grain boundary, the Ru d orbital reconstructs and results in reduction of magnetic moments and change of spin polarization along the grain boundary, forming a magnetic-nonmagnetic-magnetic junction.

“Our findings can help us to understand the past transport properties such as the negative magnetoresistance and absence of tunneling magnetoresistance at the SrRuO3 grain boundary, and also predict new effects of the SrRuO3 grain boundary such as the interfacial magnetoelectric coupling when SrRuO3 is used as a bottom electrode for growth of ferroelectric thin films,” said Professor Peng Gao, corresponding author of the study. “In a broader perspective, control of defect structure at the atomic scale can realize peculiar physical properties, providing us a new strategy to design devices with new low-dimensional magnetic properties by using boundary engineering.” [APBN]

Source: Li, X. et al. (2020). Atomic origin of spin-valve magnetoresistance at the SrRuO3 grain boundary. National science review7(4), 755-762.