Strain-Induced Superconductivity Enhancement in Co-Doped BaFe₂As₂ via Argon Ion Implantation: Evidence from Electrical and Magnetic Measurements

Introduction:
Superconductors (R=0) are excellent electrical conductors with useful magnetic properties. This has allowed many useful applications (like high-current-carrying superconducting (SC) wires) for decades. Iron-based superconductors—especially iron pnictides and chalcogenides—have recently generated attention. On one hand, they can be SC up to a high superconducting critical temperature (Tc) of 58 K in spite of the high fraction of magnetic ions (Fe), and on the other hand, they have potential as wires for high-field SC magnets. However, further enhancement of Tc remains a key research objective for practical applications.

Methods:
We explore here the effects of ion implantation on underdoped Ba(Fe₀.₉₄₃Co₀.₀₅₇)₂As₂ single crystals. Irradiation was with 1.5 MeV Ar⁶⁺ ions at a fluence of 2.5 × 10¹⁵ ions/cm². Magnetic susceptibility (both real and imaginary components) and electrical resistivity were measured before and after irradiation.

Results:
Following irradiation onset, Tc rose from 16.9 K to 25.2 K, as measured from the real part of magnetic susceptibility—a rise of 8.3 K. Comparable enhancements were seen for the imaginary part of susceptibility (8.1 K) and resistivity measurements (7.8 K). These results significantly exceed previously reported [1] Tc shift (typically <1 K) cases of similar ion irradiations in related systems.

Conclusions:
The enhancement is attributed to a compressive strain [3] induced by high-pressure Ar micro-bubbles within the implanted layer, formed at depths up to the ion range (R) under conditions where sample thickness (t) ≫ R. This strain mimics external pressure, thereby promoting superconductivity. A similar Tc emergence in undoped BaFe₂As₂ supports this pressure-driven mechanism, highlighting ion implantation as a promising approach for Tc enhancement in superconductors.

References:

[1] T. Ozaki, L. Wu, C. Zhang, J. Jaroszynski, W. Si, J. Zhou, Y. Zhu, Q. Li, Nat. Commun. 7 (2016) 13036(1-9).

[2] Kriti R Sahu, Th. Wolf, A K Mishra, Keka R. Chakraborty, A Banerjee, V Ganesan, Udayan De, Physica C: Superconductivity and its applications, 635, 1354733, 2025