Abstract
The potential applications of perovskite manganite R1-xAxMnO3 (R = rare earth element; A = Sr, Ca) thin films have been continuously explored due to their multi-functional properties. In particular, the optimally hole-doped La0.67Ca0.33MnO3 thin film demonstrates a colossal magneto-resistance that is beneficial to the performance of spintronic devices. To understand the effect of R and A ions on the material properties, we systematically measure the resistivity, magnetization, and electronic energy states for three optimally hole-doped R0.67A0.33MnO3 thin films with R = La, Sm and A = Sr, Ca. Various energy parameters are derived based on the X-ray absorption and X-ray photoelectron spectra, including the band gap, the charge frustration energy and the magnetic exchange energy. It is interesting to find that the replacement of La with Sm is more effective than that of Sr with Ca in terms of tuning the electrical property, the Curie temperature, and the band gap. The strain-induced reduction of the O 2p- Mn 3d hybridization and the interplay of R/A site disorder and strain effect are discussed. The results of this study provide useful information for the band design of perovskite oxide films.
Highlights
Perovskite manganite R1-xAxMnO3 (R = rare earth element; A = alkaline metal) has attracted long standing attention because of its fascinating properties related to the correlations between spin, charge, and orbital degrees of freedom
We report a systematic analysis on the electronic structures of R0.67A0.33MnO3 (R = La, Sm; A = Sr, Ca) thin films with X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS)
From the XPS and XAS data, we conclude that the band structures of LSMO, LCMO, and SSMO are different due to the modification of the hybridization between Mn 3d and O 2p states
Summary
From the XPS and XAS data, we conclude that the band structures of LSMO, LCMO, and SSMO are different due to the modification of the hybridization between Mn 3d and O 2p states. The obtained three energies Eg, Ecf, and Eex, as well as the orbital energy levels, are listed in Table 1 for LSMO, LCMO, and SSMO films. The temperature-dependent resistivity data show that the ground state of SSMO film is insulating while it is metallic for LSMO and LCMO films, suggesting the transport mechanism in SSMO film is different from other two samples. The strain effect on the insulator-metal temperature of SSMO film is much more significant compared with that of LSMO and LCMO films. The values of the band gap, charge fluctuation energy, and magnetic exchange energy (Eg, Ecf, Eex) are obtained as (2.6 eV, 2.1 eV, 2.9 eV) for LSMO film, (3.0 eV, 2.2 eV, 3.0 eV) for LCMO film, and (4.3 eV, 3.0 eV, 3.9 eV) for SSMO film. A large band gap of 4.3 eV in SSMO film is obtained, which may be beneficial to the wide band gap applications
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