Understanding vortex dynamics in CaK(Fe,Ni)₄As₄ and Ba(Fe,Co)₂As₂ single crystals under the influence of random point disorder

Journal Article · 26 September 2024 · Superconductor Science and Technology

DOI: https://doi.org/10.1088/1361-6668/ad7c8d · OSTI ID:2475175

Haberkorn, N.  ^[1]; Xu, M.  ^[2]; Schmidt, J. ^[3]; Suárez, S. ^[4]; Bud’Ko, S. L.  ^[3]; Canfield, P. C.  ^[3]

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1. Instituto de Nanociencia y Nanotecnología (CNEA—CONICET) (Argentina); Universidad Nacional de Cuyo and Comisión Nacional de Energía Atómica, San Carlos de Bariloche (Argentina)
2. Ames Laboratory (AMES), Ames, IA (United States); Iowa State University, Ames, IA (United States); Michigan State University East Lansing, MI (United States)
3. Ames Laboratory (AMES), Ames, IA (United States); Iowa State University, Ames, IA (United States)
4. Universidad Nacional de Cuyo and Comisión Nacional de Energía Atómica, San Carlos de Bariloche (Argentina); Comisión Nacional de Energía Atómica, San Carlos de Bariloche (Argentina)

We report on the influence of doping on vortex dynamics in 3 MeV proton-irradiated single crystals of CaK(Fe_1–xNi_x)₄As₄ (1144, x = 0.015, 0.025, and 0.03) and Ba(Fe_1–xCo_x)₂As₂ (x = 0.04, 0.062, 0.066 and 0.074). Non-irradiated crystals of the 1144 system display superconducting critical temperatures ranging from 31 K for x = 0.015–20.5 K, as doping increases to 0.03. On the other hand, pristine crystals of the 122 system show T_c values between 14.6 and 23.6 K, with the maximum T_c occurring at intermediate doping levels. The fluence was set at 3 × 10¹⁶ p cm^–2, resulting in a decrease in the T_c by around 1.5 K for all samples and significantly affecting the vortex dynamics by reducing the flux creep relaxation compared to previously reported values for unirradiated crystals. Parameters such as vortex pinning energy U₀ and the glassy exponent μ dependencies on doping and magnetic field strength are identified. For the 1144 system, U₀ reaches values approaching 500 K for small fields in samples with T_c= 29.3 K (x = 0.015), systematically decreasing to around 200 K as T_c falls below 20 K. Furthermore, U₀ decreases as the field increases to 3 T for the same sample, varying from approximately 250 K to 100 K as T_c decreases. These changes are typically accompanied by modifications in μ, gradually increasing from values around 1 towards 1.5, corresponding to small bundle relaxation in the collective creep theory. Despite differences in the substitutional disorder and magnetic phase diagram with respect to the 1144 system, the results for 122 single crystals follow a similar tendency in which U₀ usually reduces and μ increase rise as the applied magnetic field is increased. Due to moderate U₀ in these systems (few hundreds of kelvins), the resulting decay of persistent current at liquid helium temperatures is primarily determined by a balance between U₀ and bundle size contribution. Furthermore, these findings provide valuable insights for potential applications of these systems, particularly in the context of intrinsic superconducting parameters and the resulting pinning landscape.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE)
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 2475175
• Report Number(s): IS-J--11,440
• Journal Information: Superconductor Science and Technology, Journal Name: Superconductor Science and Technology Journal Issue: 11 Vol. 37; ISSN 0953-2048
• Publisher: IOP PublishingCopyright Statement
• Country of Publication: United States
• Language: English