Magnetic and superconducting properties of FeSe1-xTex (x∼0, 0.5, and 1.0)

The magnetization of FeSe1-xTex (x similar to 0, 0.5, and 1.0) compounds has been studied in magnetic fields up to 50 kOe and at temperatures of 2-300 K. The superconducting transition was observed at T-c similar to 8 K and 13.6-14.2 K in FeSe0.963 and FeSe0.5Te0.5, respectively. For most of the samples, nonlinearity of the magnetization curves in the normal state gives evidence of a common, substantial presence of ferromagnetic impurities in these compounds. By taking these impurity effects into account, the intrinsic magnetic susceptibility chi of FeSe0.963, FeSe0.5Te0.5, and FeTe was estimated to increase gradually with Te content. For FeTe a drastic drop in chi(T) with decreasing temperature was found at T-N similar to 70 K, which is presumably related to antiferromagnetic ordering. To shed light on the observed magnetic properties, ab initio calculations of the exchange enhanced magnetic susceptibility are performed for FeSe and FeTe in the local spin density approximation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552132]