Pressure Dependence of Superconducting Properties, Pinning Mechanism, and Crystal Structure of the Fe 0.99 Mn 0.01 Se 0.5 Te 0.5 Superconductor

We have investigated the pressure ( ) effect on structural (up to 10 GPa), transport [ ( ): up to 10 GPa], and magnetic [( ( ): up to 1 GPa)] properties and analyzed the flux pinning mechanism of the Fe Mn Se Te superconductor. The maximum superconducting transition temperature ( ) of 22 K with the coefficient of d /d = +2.6 K/GPa up to 3 GPa (d /d = -3.6 K/GPa, 3 ≤ ≥ 9 GPa) was evidenced from ( ) measurements. The high-pressure diffraction and density functional theory (DFT) calculations reveal structural phase transformation from tetragonal to hexagonal at 5.9 GPa, and a remarkable change in the unit cell volume is observed at ∼3 GPa where the starts to decrease, which may be due to the reduction of charge carriers, as evidenced by a reduction in the density of states (DOS) close to the Fermi level. At higher pressures of 7.7 GPa ≤ ≥ 10.2 GPa, a mixed phase (tetragonal + hexagonal phase) is observed, and the completely vanishes at 9 GPa. A significant enhancement in the critical current density ( ) is observed due to the increase of pinning centers induced by external pressure. The field dependence of the critical current density under pressure shows a crossover from the δ pinning mechanism (at 0 GPa) to the δ pinning mechanism (at 1.2 GPa). The field dependence of the pinning force at ambient condition and under pressure reveals the dense point pinning mechanism of Fe Mn Se Te . Moreover, both upper critical field ( ) and are enhanced significantly by the application of an external and change over to a high phase (hexagonal ∼5.9 GPa) faster than a Fe Ni Se Te (7.7 GPa) superconductor.