Physica B 581 (2020) 411954 Available online 18 December 2019 0921-4526/© 2019 Elsevier B.V. All rights reserved. Vortex dynamics in (NiFe 2 O 4 ) x /CuTl-1223 nanoparticles-superconductor composites S. Ahmed a , M. Zareef Khan a , K. Nadeem a , Hur Abbas a , M. Mumtaz b, * a Nanoscience and Technology Laboratory, Department of Physics, International Islamic University, Islamabad, 44000, Pakistan b Materials Research Laboratory, Department of Physics, International Islamic University, Islamabad, 44000, Pakistan A R T I C L E INFO Keywords: CuTl-1223 superconductor NiFe 2 O 4 nanoparticles (NiFe 2 O 4 ) x /CuTl-1223 composites Vortex dynamics Activation energy ABSTRACT The effect of NiFe 2 O 4 nanoparticles (NPs) addition on activation energy U o (H,T) and vortex dynamics of Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3 O 10-δ (CuTl-1223) superconducting phase was studied. Crystal structure and phase purity of CuTl-1223 matrix and NiFe 2 O 4 NPs were determined by X-ray diffraction (XRD). There was no substantial variation observed in lattice parameters of CuTl-1223 phase with inclusion of NiFe 2 O 4 NPs, which indicated the settlement of these NPs across the grain-boundaries of CuTl-1223 matrix. The broadening of superconducting resistive transition in infeld resistivity versus temperature curves was linked to thermally activated fux fow (TAFF) generating dissipation in the system. Overall decrease in U o (H,T) and vortex-glass phase transition temperature (T g ) with increasing content of NiFe 2 O 4 NPs were associated to suppression of fux pinning strength in material. The values of T g and T c Onset were shifted towards lower values with increasing content of these NPs, which was elaborated in the form of a vortex-phase diagram in H-T space. 1. Introduction The high temperature superconductors (HTSCs) have gained much attention due to their high values of critical temperature (T c ), critical current density (J c ), critical feld (H c ), long penetration depths (λ), long coherence lengths (ξ) and low anisotropy (γ). The study of HTSCs under applied magnetic feld is very important in defning their fundamental Physics towards their progressive aspects [1–3]. The superconducting resistive transition broadening of HTSCs in applied magnetic feld is a result of the vortex state having increased thermal fuctuations [4,5]. The vortex state can be separated into a low temperature vortex-solid phase and high temperature vortex-liquid phase [6–8], however these vortex-phase transitions and pinning mechanism have not been fully understood for magnetic NPs and HTSCs composites. The super- conducting Cu 0.5 Tl 0.5 Ba 2 Ca 2 Cu 3 O 10-δ (CuTl-1223) phase of CuTl-12 (n-1)n; (n ¼ 2, 3, 4, …) HTSC family is worth exploring due to its high superconducting parameters [9]. Generally, the bulk of CuTl-1223 phase is granular in nature. The inter-grains voids are the imperfections, which can suppress the superconducting properties of CuTl-1223 phase. Many research groups are constantly working on the improvement of superconducting properties of different HTSCs by enhancing their superconducting volume fraction and reducing the imperfections [10–12]. One of the most appropriate and effective techniques is the addition of nanostructures at the inter-granular spaces to reduce voids and imperfections in the bulk of HTSCs. Different methods have also been exercised to improve the effcient artifcial fux pinning centers in the bulk high temperature superconducting (HTSCs) systems but the embedding of nanostructures of suitable nature, shape and size in the bulk of HTSCs is one of the most appropriate techniques for this purpose. The pinning of magnetic fux in vortex state of HTSCs is always remained the main motivation to avoid the energy dissipation and destruction of superconducting state due to vortex dynamics in the presence of mag- netic feld when Lorentz force dominates the fux pinning force [13,14]. Different ferrites NPs have been extensively studied over the last few decades due to their number of potential applications [15–18]. The role of NiFe 2 O 4 NPs addition on superconducting transport properties of CuTl-1223 phase was already reported [19]. The suppression super- conductivity parameters of CuTl-1223 phase was observed with addition of NiFe 2 O 4 NPs, due to pair-breaking and localization of mobile charge carriers across these magnetic nanoparticles. It was found that the microscopic superconducting parameters for NiFe 2 O 4 NPs added CuTl-1223 phase theoretically deduced from excess conductivity anal- ysis were in accordance to the experimental fndings. The ac-conduction mechanism in (NiFe 2 O 4 ) x /CuTl-1223 nanoparticles-superconductor * Corresponding author. E-mail address: mmumtaz@iiu.edu.pk (M. Mumtaz). Contents lists available at ScienceDirect Physica B: Physics of Condensed Matter journal homepage: http://www.elsevier.com/locate/physb https://doi.org/10.1016/j.physb.2019.411954 Received 13 September 2019; Received in revised form 11 December 2019; Accepted 14 December 2019