Pressure Dependence of Superconductivity in FeSe studied by DC Magnetic Measurements

Abstract

Pressure dependence of superconductivity in FeSe has been investigated by DC magnetic measurements under high pressure up to 5 GPa using miniature diamond anvil cell combined with commercial SQUID magnetometer. The specimens with nominal composition FeSex (x = 0.80–1.00) were prepared from iron pieces and selenium shot firing at 1075 °C. The specimens containing no impurity phase of hexagonal FeSe were obtained for 0.80≤x≤0.96. For all of the specimens, it has been found that Tc increases in two steps by the application of pressure P, showing a local maximum of Tc∼12 K at P∼1 GPa, and Tc is nearly pressure independent above ∼3 GPa. The maximum value Tcmax above 3 GPa is 15–20 K for 0.80≤x≤0.98 but ∼25 K for x≥0.99.