Growth and superconductivity of FeSe$_{x}$ crystals

Iron selenide (FeSex) crystals with lateral dimensions up to millimeters were grown via a vapor self-transport method. The crystals consist of the dominant α-phase with trace amounts of β-phase as identified by powder x-ray diffraction. With four-probe resistance measurements, we obtained a zero resistance critical temperature of 7.5 K and a superconducting onset transition temperature of up to 11.8 K in zero magnetic field as well as an anisotropy of 1.5±0.1 for the critical field. Magnetization measurements on individual crystals reveal the coexistence of superconductivity and ferromagnetism.