Improved transport and magnetic properties of MWCNT-substituted Fe-chalcogenide system

Abstract This study investigates, for the first time in the literature, how substituting MWCNTs affects the structural, microstructural, electrical, and magnetic properties of single-crystal FeTe 0.5 Se 0.5 alloy. The MWCNTs were integrated into Fe sites in single crystalline Fe 1₋x (MWCNT) x Te 0.5 Se 0.5 (x = 0%–5%). One of our key findings is that MWCNTs dissolve well in the FeSeTe matrix up to a 4% substitution level, but beyond 3%, they appear as impurity phases within the structure. The electrical transport properties improved with increasing substitution, reaching their peak at 3%, but declined with further substitution, transforming the structure into a fully non-conductive form. The best electrical performance was obtained for the x = 3% sample with T on and T c values of 16.5 K and 15.6 K, respectively. This corresponds to a 1.7 K improvement in T c value compared to the x = 0% sample. The J c value was calculated as 1.4 × 10 5 A/cm 2 for the x = 0% and 1.1 × 10 6 A/cm 2 for the x = 3% sample, indicating a significant improvement of ~ 9.5 times. Similar improvement was also observed for the pinning force property, with F p = 2.15 × 10 6 N/m 3 for the x = 0% and F p = 4.91 × 10 7 N/m 3 for the x = 3% sample, indicating an improvement of more than 20 times. The H c2 (0) values increased with higher MWCNTs content, with the maximum H c2 (0) calculated as 78.1 T for the x = 3% sample. A notable decrease in U 0 / k B occurs as both the substitution rate and the applied field increase. This decline supports the idea that the thermally activated dissipation mechanism and independent vortex mobility are at play.