Tuning the superconducting and magnetic properties of FeySe0.25Te0.75 by varying the iron content

The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9 <= y <= 1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y < 1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y >= 1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1-xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content.