3 years ago

Spatially Resolved Large Magnetization in Ultrathin BiFeO3

Spatially Resolved Large Magnetization in Ultrathin BiFeO3
Johan van Lierop, Manuel A. Roldan, Michael R. Fitzsimmons, Andreas Herklotz, Timothy Charlton, Jonathan R. Petrie, Er-Jia Guo, Ho Nyung Lee, John W. Freeland, Qian Li, John Nichols, Sergei V. Kalinin, Ryan D. Desautels
Here, a quantitative magnetic depth profile across the planar interfaces in BiFeO3/La0.7Sr0.3MnO3 (BFO/LSMO) superlattices using polarized neutron reflectometry is obtained. An enhanced magnetization of 1.83 ± 0.16 μB/Fe in BFO layers is observed when they are interleaved between two manganite layers. The enhanced magnetic order in BFO persists up to 200 K. The depth dependence of magnetic moments in BFO/LSMO superlattices as a function of the BFO layer thickness is also explored. The results show the enhanced net magnetic moment in BFO from the LSMO/BFO interface extends 3–4 unit cells into BFO. The interior part of a thicker BFO layer has a much smaller magnetization, suggesting it still keeps the small canted AFM state. The results exclude charge transfer, intermixing, epitaxial strain, and octahedral rotations/tilts as dominating mechanisms for the large net magnetization in BFO. An explanation—one suggested by others previously and consistent with the observations—attributes the temperature dependence of the net magnetization of BFO to strong orbital hybridization between Fe and Mn across the interfaces. Such orbital reconstruction would establish an upper temperature limit for magnetic ordering of BFO. Large interfacial magnetization in BiFeO3 is observed only in close proximity (≈4 unit cells) to La0.7Sr0.3MnO3. The onset of the net magnetization in BiFeO3 occurs up to 200 K and is antiparallel to La0.7Sr0.3MnO3. Additionally, ultrathin BiFeO3 exhibits an excellent piezoresponse, providing a promising avenue for achieving the electric-field-controlled magnetism in BiFeO3-based heterostructures.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adma.201700790

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