In situ fabrication of cobalt-doped SrFe2As2 thin films by using pulsed laser deposition with excimer laser

Abstract

The remarkably high superconducting transition temperature and upper critical field of iron(Fe)-based layered superconductors, despite ferromagnetic material base, open the prospect for superconducting electronics. However, success in superconducting electronics has been limited because of difficulties in fabricating high-quality thin films.We report the growth of high-quality c-axis-oriented cobalt(Co)-doped SrFe 2 As 2 thin films with bulk superconductivity by using an in-situ pulsed laser deposition technique with a 248-nm-wavelength KrF excimer laser and an arsenic(As)-rich phase target. The temperature and field dependences of the magnetization showing strong diamagnetism and transport critical current density with superior J c -H performance are reported.These results provide necessary information for practical applications of Fe-based superconductors. \pacs{} The classes of Iron (Fe)-based superconductors [1][2][3][4][5][6][7][8] have remarkably high superconducting transition temperatures (T c ) in spite of the ferromagnetic material base; the highest T c is 55 K in LnFeAsO (FeAs-1111, Ln = lanthanide) [2] and 37.5 K in AEFe 2 As 2 (FeAs-122, AE = alkaline-earth element) [7]. The zero-temperature upper critical field (H c2 (0)) was found to be up to 65 T in the FeAs-1111 [9]. The discovery of these new classes of superconductors has regenerated interest in superconductivity because of an opportunity to tune these materials in many ways [10,11]. This potentially allows one to reveal the mechanism of high-temperature superconductors.Ever since discovering these compounds, much progress has been made in measuring the fundamental physical properties in order to understand the superconducting mechanism. However, controversy still exists because the measurements were carried out on bulk polycrystals, except for some works on single crystals [8,[12][13][14][15][16]. Highquality thin films are needed to investigate the physical properties and to develop superconducting electronic devices, such as Josephson junctions. However, controlling the stoichiometry of the FeAs-1111 phase is difficult because the crystal structure contains two different anions [17]. Also, in the FeAs-1111 phase, electrons are doped by partially replacing oxygen ions with fluorine (F), which is easily evaporated in a vacuum chamber at a high temperature because of its very high vapor pressure. These reasons make it difficult to fabricate high-quality thin film [17][18][19].Very recently, Hosono et al. reported success in growing cobalt (Co)-doped SrFe 2 As 2 thin film [18,19]. Even though this compound has a relatively lower T c , Codoping is more suitable for thin film growth than other types of doping (F or potassium (K)) because of the low vapor pressure of Co. Also, SrFe 2 As 2 contains only one anion species. Hosono et al. fabricated the thin films by using pulsed laser deposition (PLD) with a second-harmonic 532-nm-wavelength Nd:YAG laser and a stoichiometric target disk.In general, an ultraviolet (UV) wavelength is known ...

Fabrication details of Ba1-xKxFe2As2films by pulsed laser deposition technique

“…A and B are the curves of the films fabricated with different amount of potassium of 0.48 g and 0.2 g, respectively. B shows better crystallinity as compared to A, and the full width at half maximum of the (008) peak is 0.5° which is comparable with the iron based superconducting films fabricated by in situ method [11].…”

“…The method of synthesizing targets is similar to that in our previous works [9], [11]. However, the molar ratio of As is decreased from as we used in previous works, so the compositional molar ratio of Fe powder (99.9%) and As pieces (99.99%) is 2.0 and 2.4, respectively.…”

Coherent interfacial bonding on the FeAs tetrahedron in Fe/Ba(Fe1−xCox)2As2 bilayers

“…[2][3][4][5][6][7][8][9][10] However, difficulties overcoming the poor metal/oxide bond at the interface of many substrates has necessitated the need for significant optimization of the deposition parameters 9,10 as well as the use of various intermediate layers 8 to produce well-textured films. In spite of these efforts, nearly all of these films contain an unintentional amorphous or iron-containing layer at the interface.…”

Development of very high Jc in Ba(Fe1-xCox)2As2 thin films grown on CaF2

“…In fact, besides having a high H c2 , FBS have also shown high intragrain critical current density J c 1617. Despite the relatively low T c (about 22 K in the bulk form), Co-doped BaFe 2 As 2 (Ba122) has been studied by several groups1819202122 because thin film growth is relatively easy compared to other FBS materials. We previously demonstrated that Ba122 thin films have the impressive capability to accept a high density of secondary phases that act as strong pinning centres2325.…”