Near-room temperature ferromagnetic insulating state in highly distorted LaCoO<sub>2.5</sub> with CoO<sub>5</sub> square pyramids.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 33767171.
- Also identified by DOI 10.1038/s41467-021-22099-y and PMC identifier 7994406.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Dedicated control of oxygen vacancies is an important route to functionalizing complex oxide films. It is well-known that tensile strain significantly lowers the oxygen vacancy formation energy, whereas compressive strain plays a minor role. Thus, atomic reconstruction by extracting oxygen from a compressive-strained film is challenging. Here we report an unexpected LaCoO<sub>2.5</sub> phase with a zigzag-like oxygen vacancy ordering through annealing a compressive-strained LaCoO<sub>3</sub> in vacuum. The synergetic tilt and distortion of CoO<sub>5</sub> square pyramids with large La and Co shifts are quantified using scanning transmission electron microscopy. The large in-plane expansion of CoO<sub>5</sub> square pyramids weaken the crystal field splitting and facilitated the ordered high-spin state of Co<sup>2+</sup>, which produces an insulating ferromagnetic state with a Curie temperature of ~284 K and a saturation magnetization of ~0.25 μ<sub>B</sub>/Co. These results demonstrate that extracting targeted oxygen from a compressive-strained oxide provides an opportunity for creating unexpected crystal structures and novel functionalities.