Abstract
We report direct evidence of the theoretically predicted electron-rich surface of doped perovskite manganites ${\mathrm{La}}_{0.7}{A}_{0.3}{\mathrm{MnO}}_{3}\phantom{\rule{4pt}{0ex}}(A=\text{Ca}$, Sr) by means of surface-enhanced Raman spectroscopy. The required Au nanoparticles were grown on top of thin manganite films by the metalorganic aerosol deposition technique, which provides a stable oxygen atmosphere and prevents deoxygenation effects. The acquired surface-enhanced Raman spectra of rhombohedral ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ thin films reveal the symmetry-forbidden Jahn-Teller stretching modes demonstrating the predicted symmetry breaking at the surface and fallback into the orthorhombic (Pnma) structure. This results in a unique Jahn-Teller reconstructed surface structure, which limits the capabilities of mixed-valence manganites in spintronic applications, but will be highly favorable for catalytic reactions.
Highlights
Mixed-valence perovskite manganites, such as La1−xAxMnO3 (A = Sr, Ca), possess strong electron-spinlattice correlations [1,2], which result in many fundamentally interesting and useful electronic properties
The high partial oxygen pressure, p(O2) ≈ 0.2 bar, within the metalorganic aerosol deposition (MAD) prevents or at least minimizes the formation of oxygen vacancies during the deposition
Since the thickness is much smaller than 8 nm, one could expect a strong reduction of the TC and TMM, because of deoxygenation
Summary
Segregation effects, which are well known in manganite thin films [23,24], lower the effective doping at the surface and can result in the reconstruction of the surface layer, forming a Ruddleson-Popperlike phase [25] or in a change of the manganese valence, as shown in La1−xPbxMnO3 [26] In the latter case, the valence change was attributed to the possible higher oxidation states of Pb, compared to Sr or Ca. In the latter case, the valence change was attributed to the possible higher oxidation states of Pb, compared to Sr or Ca These extrinsic segregation effects are related to oxygen deficiencies and depend on the growth conditions, i.e., temperature and oxygen partial pressure [27,28]. To the best of our knowledge, only one TERS study on a strongly correlated material, the double perovskite La2CoMnO6 [43], was published, but no surface-oriented studies of the mixed-valence manganites, La1−xAxMnO3, were reported up to now In this Rapid Communication, we present a SERS study on thin La0.7Ca0.3MnO3 (LCMO) and La0.7Sr0.3MnO3 (LSMO) films. This gives evidence for the presence of the cooperative JT effect due to the symmetry-breaking-induced electron enrichment at the LSMO surface
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
