High Jc and low anisotropy of hydrogen doped NdFeAsO superconducting thin film

Abstract

The recent realisations of hydrogen doped LnFeAsO (Ln = Nd and Sm) superconducting epitaxial thin films call for further investigation of their structural and electrical transport properties. Here, we report on the microstructure of a NdFeAs(O,H) epitaxial thin film and its temperature, field, and orientation dependencies of the resistivity and the critical current density Jc. The superconducting transition temperature Tc is comparable to NdFeAs(O,F). Transmission electron microscopy investigation supported that hydrogen is homogenously substituted for oxygen. A high self-field Jc of over 10 MA/cm2 was recorded at 5 K, which is likely to be caused by a short London penetration depth. The anisotropic Ginzburg–Landau scaling for the angle dependence of Jc yielded temperature-dependent scaling parameters γJ that decreased from 1.6 at 30 K to 1.3 at 5 K. This is opposite to the behaviour of NdFeAs(O,F). Additionally, γJ of NdFeAs(O,H) is smaller than that of NdFeAs(O,F). Our results indicate that heavily electron doping by means of hydrogen substitution for oxygen in LnFeAsO is highly beneficial for achieving high Jc with low anisotropy without compromising Tc, which is favourable for high-field magnet applications.

New Scaling Laws for Pinning Force Density in Superconductors

“…To demonstrate that the → F p (B, J c ) dataset for the MgB 2 thin film (shown in Figure 1) represents a typical dataset for superconducting films, we fitted the projection of this dataset into the X = 0 plane, that is, → F p (B) , to Equation (3) in Figure 2b. The deduced parameters p = 0.45 ± 0.03 ∼ = 0.5 and q = 2.3 ± 0.5 ∼ = 2 certainly represent typical characteristic values that are often deduced from the → F p (B) fits to Equation (3) [11,25,26].…”

“…This is the primary reason for the widely accepted deduction [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]24,25] of the pparameter of Equation (3), which is the primary value in Kramer-Dew-Hughes scaling laws [2,3]…”

Fabrication of microstrips of iron-based superconductor NdFeAs(O,H)

“…Recently, a method to substitute H for O in LnFeAsO thin films by a topotactic reaction using CaH 2 has been reported [35]. Referring to this report, we have fabricated NdFeAs(O,H) thin films with a T c comparable to and a J c (>17 MA cm −2 ) higher than NdFeAs(O,F) thin films [36,37]. These NdFeAs(O,H) thin films do not have a covering layer on the superconducting film that hinders photon detection.…”

Recent progress on epitaxial growth of Fe-based superconducting thin films

“…The depth profile by SIMS for the SmFeAs(O,H) thin film showed inhomogeneous doping of H. The H content with respect to oxygen decreased from 0.34 at the surface to 0.1 at the film/substrate interface. An effective method to avoid such inhomogeneous H doping is decreasing the film thickness, which was proved by the microstructural analysis by transmission electron microanalysis (TEM), shown in figure 4 [12]. The 24 nm thick NdFeAs(O,H) film is microstructurally clean (figure 4(a)).…”

“…Since the film is microstructurally clean (figure 4(a)), J c decreased rather quickly with field. As discussed in [12], the high J c may be due to the short penetration depth λ by heavy electron doping, although the direct evidence is still missing. Recently, considerable improvement of J c by over-doping has been reported for YBa 2 Cu 3 O y [73].…”