Thin film growth by pulsed laser deposition and properties of 122-type iron-based superconductor AE(Fe1−xCox)2As2(AE=alkaline earth)

This paper reports comprehensive results on thin film growth of 122-type iron-pnictide superconductors, AE(Fe 1− x Co x ) 2 As 2 (AE= Ca, Sr, and Ba, AEFe 2 As 2 :Co) by a pulsed laser deposition method using a neodymium-doped yttrium aluminum garnet laser as an excitation source. The most critical parameter to produce the SrFe 2 As 2 :Co and BaFe 2 As 2 :Co phases is the substrate temperature ( T s ). It is difficult to produce highly pure CaFe 2 As 2 :Co phase thin film at any T s . For BaFe 2 As 2 :Co epitaxial films, controlling T s at 800–850 °C and growth rate to 2.8–3.3 Å s −1 produced high-quality films with good crystallinity, flat surfaces, and high critical current densities > 1 MA cm −2 , which were obtained for film thicknesses from 100 to 500 nm. The doping concentration x was optimized for Ba(Fe 1− x Co x ) 2 As 2 epitaxial films, leading to the highest critical temperature of 25.5 K in the epitaxial films with the nominal x = 0.075.