Critical factor for epitaxial growth of cobalt-doped BaFe2As2 films by pulsed laser deposition

Abstract

We heteroepitaxially grew cobalt-doped BaFe 2 As 2 films on (La,Sr)(Al,Ta)O 3 single-crystal substrates by pulsed laser deposition using four different wavelengths and investigated how the excitation wavelength and pulse energy affected growth. Using the tilting and twisting angles of X-ray diffraction rocking curves, we quantitatively analyzed the crystallinity of each film. We found that the optimal deposition rate, which could be tuned by pulse energy, was independent of laser wavelength. The high-quality film grown at the optimal pulse energy (i.e., the optimum deposition rate) exhibited high critical current density over 1 MA/cm 2 irrespective of the laser wavelength.

Vortex Pinning Properties of Phosphorous-Doped <inline-formula> <tex-math notation="TeX">$\hbox{BaFe}_{2}\hbox{As}_{2}$</tex-math></inline-formula> Epitaxial Films: Comparison Between <inline-formula> <tex-math notation="TeX">$(\hbox{La},\hbox{Sr})(\hbox{Al},\hbox{Ta})\hbox{O}_{3} $</tex-math></inline-formula> and MgO Substrates

“…The in-plane lattice mismatch [(a substrate − a Ba122:P )/a Ba122:P , where a Ba122:P is a-axis length of the single crystal with the same chemical composition] between BaFe 2 As 2 : P and LSAT (a = 3.86 Å) is smaller (−1.8%) than that between BaFe 2 As 2 : P and MgO (a = 4.21 Å) (+6.9%), but the crystallinity of BaFe 2 As 2 : P/LSAT was poorer than that of BaFe 2 As 2 : P/MgO. This result suggests the presence of a larger number of defects than for BaFe 2 As 2 : P/MgO and/or a chemical reaction between LSAT and BaFe 2 As 2 : P, similar to the case of Ba(Fe, Co) 2 As 2 on LSAT [16].…”

“…This film had no pinning centers along the c-axis and exhibited a vortex pinning anisotropy similarly to that of single crystals. On the other hand, Katase et al succeeded in fabricating Ba(Fe, Co) 2 As 2 epitaxial films directly on LSAT and MgO (001) single-crystal substrates without buffer layers by optimizing the growth condition [13]- [16]. These films exhibited strong vortex pinning along the c-axis [17], [18], which is comparable to those of the above films employing the buffer layers, originating from vertical defects in the films.…”

Enhanced critical-current in P-doped BaFe2As2 thin films on metal substrates arising from poorly aligned grain boundaries

“…Both images show a clear stacked structure composed of the Ba122:P film, epitaxial MgO, IBAD-MgO, Y 2 O 3 , and Hastelloy substrate, where deterioration of each layer was not detected irrespective of the high temperature growth (1050 °C). In contrast to a Ba122:Co film fabricated by low-power KrF excimer laser PLD45, horizontal defects such as stacking faults are not observed in the present films, indicating that the peaks along the ab planes in the J c ‒ θ H plots mainly originate from the intrinsic electronic anisotropy of Ba122:P. In addition, J c values for H // ab at 4 K of the Ba122:P film on poorly aligned IBAD-MgO are higher than those of Ba122:P film on well-aligned aligned IBAD-MgO (see Fig. 3(c)).…”

Iron pnictide thin films: Synthesis and physics

“…Co‐doped BaFeAs films can be grown by UHV‐PLD on different substrates and upon a relatively broad window of deposition parameters. It was furthermore shown in a recent study that the film quality of BaFeAs does not depend on the laser wavelength that is used for target ablation, however the energy of the laser pulse has decisive influence on the optimal growth rate (). Film growth at IFW Dresden was performed using a KrF excimer laser (= 248 nm) with energy densities on the target between 3 and 5 J cm.…”