Control of interstitial Fe and its impact on superconductivity of FeTe_1/2Se_1/2

The FeTe_1/2Se_1/2 samples are quenched during the vacuum sealed synthesis process to room temperature from 700°C, 500°C, 300°C and room temperature (RT); named as 700Q, 500Q, 300Q and RTQ respectively. Though all samples except 700Q are crystallized in single phase with space group P4/nmm, the presence of interstitial Fe (_Feint) at 2c site is increased from 5% for RTQ to 8% for 500Q. The 700Q sample is crystallized in Fe₇Se₈ phase. Also though the RTQ and 300Q are superconducting at 10 K and 13 K respectively, the 500Q and 700Q are not. Magnetic ordering (T_mag) is observed at around 125 K for all the samples. The prominence of T_mag in terms of effective moment is sufficiently higher for 500Q and 700Q than RTQ and 300Q. Summarily, it is found that quenching induced disorder affects the occupancy of Fe_int in FeTe_1/2Se_1/2 and thus both its superconducting and magnetic properties.