Ternary metal‐oxide material systems commonly crystallize in the perovskite crystal structure, which is utilized in numerous electronic applications. In contrast to oxides, there are no known nitride perovskites, likely due to the competition with oxidation, which makes the formation of pure nitride materials difficult and synthesis of oxynitride materials more common. While deposition of oxynitride perovskite thin films is important for many electronic applications, it is difficult to control oxygen and nitrogen stoichiometry. Lanthanum tungsten oxynitride (LaWN3−
Spin‐state transitions are an important research topic in complex oxides with the diverse magnetic states involved. In particular, the low‐spin to high‐spin transition in LaCoO3thin films has drawn a wide range of attention due to the emergent ferromagnetic state. Although various mechanisms (e.g., structural distortion, oxygen‐vacancy formation, spin‐state ordering) have been proposed, an understanding of what really underlies the emergent ferromagnetism remains elusive. Here, the ferromagnetism in LaCoO3thin films is systematically modulated by varying the oxygen pressure during thin‐film growth. Although the samples show dramatic different magnetization, their cobalt valence state and perovskite crystalline structure remain almost unchanged, ruling out the scenarios of both oxygen‐vacancy and spin‐ordering. This work provides compelling evidence that the tetragonal distortion due to the tensile strain significantly modifies the orbital occupancy, leading to a low‐spin to high‐spin transition with emergent ferromagnetism, while samples grown at reduced pressure demonstrate a pronounced lattice expansion due to cation‐off‐stoichiometry, which suppresses the tetragonal distortion and the consequent magnetization. This result not only provides important insight for the understanding of exotic ferromagnetism in LaCoO3thin films, but also identifies a promising strategy to design electronic states in complex oxides through cation‐stoichiometry engineering.
more » « less- Award ID(s):
- 2102895
- NSF-PAR ID:
- 10400997
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Advanced Electronic Materials
- Volume:
- 9
- Issue:
- 5
- ISSN:
- 2199-160X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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