TY - JOUR
T1 - Electrical resistivity anomaly, valence shift of Pr ion, and magnetic behavior in epitaxial (Pr1-yYy)1-xCaxCoO3 thin films under compressive strain
AU - Fujishiro, H.
AU - Noda, Y.
AU - Akuzawa, K.
AU - Naito, T.
AU - Ito, A.
AU - Goto, T.
AU - Marysko, M.
AU - Jirak, Z.
AU - Hejtmanek, J.
AU - Nitta, K.
N1 - Funding Information:
The synchrotron radiation experiments were performed at the BL01B1 of SPring-8 with approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal Nos. 2013A1093 and 2016B1089). The authors thank Dr. T. Ina of JASRI for his experimental assistance for XRF measurements. This work was partly supported by JSPS KAKENHI (Grant No. 24540355) and was performed under the Inter-university Cooperative Research Program of the Institute for Materials Research, Tohoku University. The work at Institute of Physics, Prague, was supported by Project No. 17-04412S of the Czech Science Foundation.
Publisher Copyright:
© 2017 Author(s).
PY - 2017/3/21
Y1 - 2017/3/21
N2 - We have fabricated (Pr1−yYy)1-xCaxCoO3 (PYCCO) epitaxial films with various thicknesses by pulsed laser deposition on the SrLaAlO4 (SLAO) substrate that applied an in-plane compressive stress to the film, and investigated the temperature dependence of the electrical resistivity, ρ(T), of the films. An anomalous ρ(T) upturn with a broad hysteresis could be clearly observed only for the thinnest film (d = 50 nm), and the ρ(T) anomaly decreased by increasing film thickness, d. The temperature dependence of the X-ray absorption near-edge structure (XANES) spectra at Pr L2-edge was measured for the films, and the valence states of praseodymium (Pr) ion were determined using the analysis of the XANES spectra. As a result, the average valence of the Pr ion in the d = 50 nm film slightly increases with decreasing temperature from the common value of 3.0+ around room temperature to 3.15+ at 8 K. The valence shift of Pr is thus similar to what was observed on the PYCCO polycrystalline bulks with an abrupt metal-insulator transition, accompanied by a spin-state (SS) transition of Co ions. Furthermore, the low-temperature SQUID measurements evidenced a paramagnetic behavior down to the lowest temperature, which suggests that the dominant part of Co3+ ions in the film grown on the SLAO substrate tends to be in the low spin state characteristic for the insulating ground state. These results strongly suggest that the anomalous ρ(T) upturn in the thin films on the SrLaAlO4 (SLAO) substrate is closely related to the SS transition of Co ions. On the other hand, PYCCO films grown on the LaAlO3 (LAO) substrate that applied an in-plane tensile stress showed no valence shift of Pr ions and developed a long range ferromagnetic order, which points to a complete suppression of the low-temperature transition. The behaviors of the epitaxial films are discussed in terms of the in-plane stress exerted by different substrates and accumulated elastic energy.
AB - We have fabricated (Pr1−yYy)1-xCaxCoO3 (PYCCO) epitaxial films with various thicknesses by pulsed laser deposition on the SrLaAlO4 (SLAO) substrate that applied an in-plane compressive stress to the film, and investigated the temperature dependence of the electrical resistivity, ρ(T), of the films. An anomalous ρ(T) upturn with a broad hysteresis could be clearly observed only for the thinnest film (d = 50 nm), and the ρ(T) anomaly decreased by increasing film thickness, d. The temperature dependence of the X-ray absorption near-edge structure (XANES) spectra at Pr L2-edge was measured for the films, and the valence states of praseodymium (Pr) ion were determined using the analysis of the XANES spectra. As a result, the average valence of the Pr ion in the d = 50 nm film slightly increases with decreasing temperature from the common value of 3.0+ around room temperature to 3.15+ at 8 K. The valence shift of Pr is thus similar to what was observed on the PYCCO polycrystalline bulks with an abrupt metal-insulator transition, accompanied by a spin-state (SS) transition of Co ions. Furthermore, the low-temperature SQUID measurements evidenced a paramagnetic behavior down to the lowest temperature, which suggests that the dominant part of Co3+ ions in the film grown on the SLAO substrate tends to be in the low spin state characteristic for the insulating ground state. These results strongly suggest that the anomalous ρ(T) upturn in the thin films on the SrLaAlO4 (SLAO) substrate is closely related to the SS transition of Co ions. On the other hand, PYCCO films grown on the LaAlO3 (LAO) substrate that applied an in-plane tensile stress showed no valence shift of Pr ions and developed a long range ferromagnetic order, which points to a complete suppression of the low-temperature transition. The behaviors of the epitaxial films are discussed in terms of the in-plane stress exerted by different substrates and accumulated elastic energy.
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U2 - 10.1063/1.4978747
DO - 10.1063/1.4978747
M3 - Article
AN - SCOPUS:85016138267
VL - 121
JO - Journal of Applied Physics
JF - Journal of Applied Physics
SN - 0021-8979
IS - 11
M1 - 115104
ER -