Effects of oxygen ion implantation on single-crystalline MgB2 thin films

Abstract

We studied the effects of oxygen (O) ion irradiation on superconducting properties of single-crystalline MgB2 thin films with various thicknesses (130, 410, 850, and 1300 nm). Low irradiation energy was used to implant ions into the films. The correlation thickness of the top-implanted layer and the thickness of the bottom-clean layer could be adjusted by controlling irradiating energy. An interesting exponential dependence of Tc on the thickness ratio of these layers was found possibly due to the conventional proximity effect. The MgO, which is known as an effective pinning source for MgB2, was induced in implanted films. Thus, despite the use of low irradiation energy, the field performance critical current density, Jc(H), was significantly improved in most cases of irradiated films. The pinning force density (Fp) showed a crossover from surface pinning to a normal point pinning mechanism. These results indicate that the superconducting and the pinning mechanism in single-crystalline MgB2 could be well managed by the oxygen ion implantation.

Angle-dependent Hall effect and vortex dynamics in single-crystalline MgB2 thin films

“…In order to investigate the effect of pinning on the scaling behavior, the field-sweep Hall scaling at 15 K of samples with different irradiation doses was plotted and shown in figure 2. By varying the irradiation dose, the defects density and flux pinning strength of MgB 2 films change as well [15,19]. The scaling exponent β=2±0.2 holds even after various doses of irradiation.…”

“…is the angle-dependent anisotropy parameter, which is the main parameter describing the angular dependencies of physical quantities in an anisotropic superconductor. κ is the GL parameter, which was expected to remain unchanged with low energy irradiation, since the Δκ pinning does not take place in irradiated MgB 2 films [15]. Ĥc1 is the lower critical field along the c-axis and H c2 (θ)=Φ 0 /(2 πγ(θ) ξ 2 ) upper critical field along θ.…”

“…Generally, the electron mean free path (l) in irradiated samples decreases and, consequently, the coherence length (ξ), leading to an increasing of H c2 [28]. Recently, we have reported significant enhancements of H c2 and critical current density (J c ) in low energy ion irradiated MgB 2 films [15,19]. In this work, by increasing the irradiation dose, H c2 was certainly shown to be enhanced as well (as shown in inset of figure 5(a)), leading to increased Δ θ .…”

“…The detailed fabrication process of the HPCVD system has been previously described elsewhere [14]. The high-quality of the thin films was confirmed in our previous study [15]. The Fe irradiation process was carried out in the Korea Multi-purpose Accelerator Complex (KOMAC).…”

Effects of irradiation on superconducting properties of small-grained MgB2 thin films

“…6(d), [47] in general, single-crystalline MgB 2 films showed the dominance of normal point pinning after low-energy ion irradiation. [48,49] The effect of GBs on the irradiation-induced defects in the relatively thicker MgB 2 films with a thickness of 430 nm (MB430) was additionally studied in comparison with the thickness of the irradiated regions. The XRD results of the MB430 are shown in Fig.…”