The significant magnetic attenuation with submicrometer scale magnetic phase separation in tensile-strained LaCoO3 films

It is well known that the epitaxial strain plays a vital role in tuning the magnetic states in transition metal oxide LaCoO3 films. Here, we reported a robust long-range ferromagnetic (FM) ground state in a tensile-strained perovskite LaCoO3 film on a SrTiO3 (STO) substrate, which has a very significant attenuation when the thickness ranges from 10 to 50 nm. It is speculated that such attenuation may be caused by the appearance of the cross-hatched grain boundary, which relaxes the tensile strain around the crosshatch, resulting in the local non-FM phases. Magnetic force microscope observation reveals non-FM patterns correlated with the structural crosshatches in the strain-relaxed film even down to a temperature of 2 K and up to a magnetic field of 7 T, suggesting the phase separation origin of magnetization attenuation. Furthermore, the investigations of the temperature-dependent inverse magnetic susceptibility show a deviation from the Curie-Weiss law above the transition temperature in a 50-nm-thick LaCoO3 /STO film but not in the LaCoO3 /LaAlO3 film, which is ascribed to the Griffiths phase due to the crosshatch-line grain boundaries. These results demonstrated that the local strain effect due to structural defects is important to affect the ferromagnetism in strain-engineered LaCoO3 films, which may have potential implications for future oxide-based spintronics. (c) 2023 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(http://creativecommons.org/licenses/by/4.0/).

Automated summary

The epitaxial strain has a significant influence on the magnetic states of LaCoO3 films. In this study, a robust long-range ferromagnetic ground state is observed in a tensile-strained LaCoO3 film on a SrTiO3 substrate, but the ferromagnetic state significantly attenuates when the film thickness is between 10 and 50 nm. The attenuation is speculated to be caused by the appearance of cross-hatched grain boundaries, which relax the tensile strain and result in local non-ferromagnetic phases. Magnetic force microscope observation confirms the correlation between non-ferromagnetic patterns and structural crosshatches, even at low temperatures and high magnetic fields, suggesting phase separation as the origin of magnetization attenuation.