Enhanced critical current density in BaFe₂(As_0.66P_0.33)₂ nanocomposite superconducting films

Abstract

The high upper critical field and low anisotropy of the 122-type iron-based superconductor BaFe2As2 makes it promising for use in superconducting high field magnets. However, its critical current density (J c) in high magnetic fields needs to be further improved. Here we show that for the film prepared by pulsed laser deposition method by controlling the deposition parameters (higher substrate temperature and lower growth rate), the crystallinity of BaFe2(As0.66P0.33)2 (Ba122:P) matrix is improved while maintaining a high density of incoherent BaZrO3 (BZO) nanoparticles (NPs) which together lead to significantly increased self field J c. Our Ba122:P nanocomposite films also exhibit increased in-field J c, reduced angular anisotropy of J c and reduced detrimental effects of thermal fluctuations (creep rate) over a wide range of temperatures and magnetic field strength. The BZO NP doped Ba122:P films show high in-field J c over 2.1 MA cm−2 even at 4 K and 9 T (μ 0 H∣∣c), which is significantly higher than that of standard Ba122:P films and conventional alloy superconducting wires. To understand the contribution of the various pinning centers, we applied a simple model, which was developed for cuprates, to Ba122:P film with all the parameters used derived by fitting to a limited set of experimental data (no free parameters) such that temperature, angle and field properties at other experimental conditions are then calculated. This simple model fits very well to the experimental results in these two very different material systems. We discuss the effectiveness of natural defect and BZO NPs on the ratio of J c to the depairing current density. The superconducting properties for 122-type iron-based superconductors obtained through this work are considered promising for high-field applications.

Thermodynamic approach for enhancing superconducting critical current performance

“…Here we display Jc s.f. as a function of Jd at 4.2 K [43][44][45][46][47][48][49][50][51][52]. Details of the calculation parameters for Jd and experimentally obtained Jc are shown in SI, Table S3.…”

Preface to the special issue ‘Focus on 10 Years of Iron-Based Superconductors’

“…A decade since the seminal work by the Hideo Hosono group, the technology is maturing in the fabrication of different kinds of samples, all of which are considered in this focus issue, namely thin films [58,59,66,70,71], coated conductors [64], single crystals [61,67,69], polycrystals [60,72] and tapes [62].…”

“…10 years after the discovery of superconducting properties in iron-based compounds, this special issue of Superconductor Science and Technology is focused on research development toward applications, with particular attention to the inter-and intra-granular critical current density [58][59][60][61][62][63][64][65][66] and the exploration of strategies to improve it [59,60,67,68].…”

“…Soon after the discovery of unconventional high-temperature superconductivity in iron-based compounds, the richness of possibilities to synthesize such compounds became apparent. Different families of iron-based superconductors are represented in this focus issue, both the most commonly studied ones, such as 122 chalcogenides [69] and pnictides [59][60][61][62]67], 1111 oxypnictides [66,70] and 11 chalcogenides [64,67,71], as well as the less-studied 21311 pnictides [72].…”

“…Regarding the strategies to improve pinning properties, Miura et al demonstrated further enhancement of J c , decreased J c anisotropy, and limited creep rates by incoherent BaZrO 3 nanoparticles with tunable density and size in BaFe 2 (As 0.66 P 0.33 ) 2 films over a wide range of temperatures and magnetic field. They achieved a self-field J c ~7.2 MA cm −2 at 5 K, which is a sizeable 15% of the depairing current, and J c ~2.1 MA cm −2 at 5 K and 9 T (µ 0 H||c) [59]. Regarding the grain boundary angle θ GB dependence of transport properties, Iida and coworkers [66] carried out a study on NdFeAs(O,F) films on MgO bicrystals.…”