Effects of Deposition Temperature on the Structural and Physical Properties of Ba(Fe1.8Co0.2)2As2 Thin Film

Ba(Fe1.8Co0.2)2As2 thin films have been grown directly on (001) SrTiO3 (STO) substrates by pulsed laser deposition at the temperatures from 640 to 700 ∘C. Effects of deposition temperature (Ts) on the structure, magnetic, and superconducting properties of the films are investigated systematically. It is found that Ba(Fe1.8Co0.2)2As2 film grown at lower deposition temperature is polycrystalline, and the optimized temperature of 685 ∘C can yield high-quality epitaxial Ba(Fe1.8Co0.2)2As2 film. The (002) diffraction peak of Fe metal at 2𝜃 =∼ 65∘ is observed along with the (00l) diffraction peaks of Ba(Fe1.8Co0.2)2As2 films deposited at all temperatures, which is attributed to the decomposition of BaFe1.8Co0.2As2 target when a high-energy pulsed laser hit on the target in a high vacuum. X-ray photoelectron spectra of Fe 2p show that the relative percentage of zerovalent ion (Fe0) is almost equal to that of divalent ion (Fe2+) for the film deposited at 670 ∘C, which is different from that most Fe2+ ions exist in the BaFe1.8Co0.2As2 target. The saturation magnetization (Ms) increases from 7.88 to 240.5 emu/cm3 monotonously with the increase of Ba(Fe1.8Co0.2)2As2 film deposition temperature. The maximum zero-resistance temperature (Tc0)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$T_{\mathrm {c}}^{0})$\end{document} of ∼16 K was obtained, which can be attributed to the high quality of the Ba(Fe1.8Co0.2)2As2 film. The coexistence of superconductivity (SC) and ferromagnetism (FM) in the BaFe1.8Co0.2As2 films was discussed.