Longitudinal Field Muon Spin Rotation Study of Magnetic Freezing in Fe Rich FeSe0.25Te0.75

We study the freezing of magnetic fluctuations in an Fe rich sample of the “11” iron-based superconductor using longitudinal field muon spin relaxation. The magnetic relaxation rate peaks at 15 K indicating spin glass freezing that nearly coincides with the superconducting transition of the corresponding Fe stoichiometric phase. At this temperature, the magnetic field dependence of the relaxation indicates slow magnetic fluctuations on the nanosecond timescale.