Critical current density (Jc) is one of the major limiting factors for high field applications of iron-based superconductors.Here, we report that Mn-ions are successfully incorporated into nontoxic superconducting (Li,Fe)OHFeSe films.Remarkably, the Jc is significantly enhanced from 0.03 to 0.32 MA/cm 2 under 33 T, and the vortex pinning force density monotonically increases up to 106 GN/m 3 , which is the highest record so far among all iron-based superconductors. Our results demonstrate that Mn incorporation is an effective method to optimize the performance of (Li,Fe)OHFeSe films, offering a promising candidate for high-field applications.Recently, elemental Mn has been incorporated into FeSe-11111 single crystals without obvious detriment to its Tc [20], which may provide an effective candidate. Moreover, iron-based superconductors in the form of films usually present a higher Jc than that of bulk samples [6,8].Therefore, it is worthy introducing transition metal ions into FeSe-11111 crystalline superconducting film for further optimization of their high-field performance.In this letter, we successfully introduced Mn-ions into a superconducting FeSe-11111 film synthesized through the so-called 2 matrix-assisted hydrothermal epitaxy (MHE) method [12]. A significant enhancement of Jc was observed in FeSe-11111 films by Mn-doping, increasing it tenfold from 0.03 to 0.32 MA/cm 2 under 33 T at 5 K. Remarkably, the vortex pinning force density (Fp) of Mndoped films monotonically increases to 106 GN/m 3 . To the best of our knowledge, this is the highest record so far among all iron-based superconducting systems. By analyzing Fp versus magnetic fields, we find the apparent enhancement of Jc in the Mn-doped FeSe-11111 film stems from the extra pinning centers induced by Mn doping.
ExperimentsThe pure and Mn-doped FeSe-11111 films were synthesized via the MHE method that we developed [12]. The x-ray diffraction (XRD) experiments were carried out on a 9 kW Rigaku SmartLab X-ray diffractometer. The scanning electron microscope (SEM) and energy dispersive X-ray (EDX) spectroscopy measurements were performed on a Hitachi SU5000. The electron energy loss spectroscopy (EELS) data were acquired using a transmission electron microscope (ARM200F, JEOL Inc.) equipped with a Gatan Quantum ER 965 Imaging Filter. Electrical transport measurements within 9T were collected with the standard four-probe method on a Quantum Design PPMS-9 system. The values of Jc were obtained using the criteria of 1 μV on I-V curves and the parameters of bridge were characterized by SEM. The high-field experiments up to 33 T were performed on the Steady High Magnetic Field Facilities, High Magnetic Field Laboratory, CAS.