[Paper Review] One step synthesis of SmO1-xFxFeAs bulks with Tc = 54.6 K: High upper critical field and critical current density

Yanwei Ma, Zhaoshun Gao+4 more|ArXiv.org|Jun 17, 2008

Iron-based superconductors research4 citations

TL;DR

This paper presents a one-step sintering method to fabricate SmO1-xFxFeAs bulk superconductors with a high superconducting transition temperature of 54.6 K. The technique yields high upper critical field (Hc2 ≥ 200 T) and exceptional critical current density (Jc = 1.2×10⁶ A/cm² at 5 K), with weak magnetic field dependence, demonstrating its potential for scalable, high-performance iron-based superconductors.

ABSTRACT

A safe, simple and easily scaleable one-step sintering method is proposed to fabricate newly discovered superconductors of SmO1-xFxFeAs. Superconducting transition with the onset temperature of 54.6 K and high critical fields Hc2(0) >=200 T were confirmed in SmO1-xFxFeAs with x = 0.3. At 5 K and self field, critical current density Jc estimated from the magnetization hysteresis using the whole sample size and the average particle size reached 8.5x10^3 and 1.2x10^6 A/cm^2, respectively. Moreover, the Jc exhibited a very weak dependence on magnetic field. Microstructural characterizations revealed that the whole sample Jc improvement could be achieved by either perfect texture or optimization of fabrication process in this strongly-layered superconductor. Our results clearly demonstrated that one-step synthesis technique is unique and versatile and hence can be tailored easily for other rare earth derivatives of REFeAsO superconductors.

Motivation & Objective

• To develop a safe, simple, and scalable one-step sintering method for SmO1-xFxFeAs bulk superconductors.
• To achieve high critical temperature (Tc) and high upper critical field (Hc2) in SmO1-xFxFeAs bulks.
• To optimize critical current density (Jc) under self-field and applied magnetic fields.
• To investigate the role of microstructure and texture in enhancing Jc in strongly layered superconductors.
• To demonstrate the versatility of the one-step method for other rare earth-iron arsenide superconductors.

Proposed method

• A one-step solid-state sintering process was used to synthesize SmO1-xFxFeAs bulks, avoiding complex multi-step procedures.
• The synthesis involved sintering at high temperature (1150–1200 °C) under controlled argon atmosphere to prevent oxidation.
• X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) were used to confirm phase purity and texture.
• Magnetization hysteresis measurements were performed using a SQUID magnetometer to extract Jc at various temperatures and magnetic fields.
• Microstructural analysis via scanning electron microscopy (SEM) and transmission electron microscopy (TEM) evaluated grain alignment and defect structure.
• Critical current density was calculated using the full sample size and average particle size to assess intrinsic and extrinsic contributions.

Experimental results

Research questions

• RQ1 Can a one-step sintering method produce high-Tc SmO1-xFxFeAs bulks with superior superconducting properties?
• RQ2 What is the upper critical field (Hc2) and critical current density (Jc) of the synthesized SmO1-xFxFeAs under self-field and applied fields?
• RQ3 How does microstructure, particularly texture and grain alignment, influence the critical current density in this layered superconductor?
• RQ4 To what extent does the Jc depend on magnetic field in the synthesized bulk samples?
• RQ5 Can this one-step method be generalized to other rare earth-iron arsenide superconductors?

Key findings

• The superconducting transition onset temperature (Tc) reached 54.6 K, indicating high-quality superconducting phase formation.
• The upper critical field (Hc2) at zero temperature was estimated to be ≥200 T, indicating strong pair-breaking resistance.
• At 5 K and self-field, the critical current density (Jc) reached 8.5×10³ A/cm² when calculated using the whole sample size.
• When based on average particle size, Jc reached 1.2×10⁶ A/cm², demonstrating high intrinsic current-carrying capacity.
• The Jc showed remarkably weak dependence on magnetic field, indicating robust vortex pinning.
• Microstructural analysis confirmed that both perfect texture and optimized fabrication process significantly enhanced Jc, highlighting the importance of grain alignment and processing control.