Effects of Three-Dimensional Strain on LaCoO₃ Thin Films

LaCoO₃ films grown on SrTiO₃ substrates are known to exhibit a net moment below T = 85 K while the same films grown on LaAlO₃ exhibit little to no moment [1]. The underlying mechanisms behind this net moment are poorly understood, but it is speculated that modulation of the Co-O-Co bond angle through epitaxial strain may play a key role. By growing LaCoO₃ films on SrTiO₃ substrates with a high angle (~ 7-9°) of miscut via pulsed laser deposition (PLD), we have been able to induce epitaxial strain along the in plane and out of plane film axes. In-situ reflection high energy electron diffraction (RHEED) detected layer-by-layer growth. Sample crystallinity and topography were measured using X-ray diffraction and atomic force microscopy, respectively. Magnetometry data were collected both parallel and perpendicular to the SrTiO₃ [100] surface, as well as parallel and perpendicular to 5 nm steps induced by the miscut of the substrate. In films of thickness ~3-10 nm grown on high angle miscut SrTiO₃ substrates, we measure a strong anisotropic magnetization in the plane where spins are realigned at low magnetic fields. Possible mechanisms will be discussed.

1. Y. Li, S. J. Peng et al., AIP Advances 8, 056317 (2018).