Effect of excess Fe on magnetic properties and crystallographic phases in Fe1+δTe

To elucidate the effect of the excess Fe on the physical properties in Fe_1+δTe, we have grown single crystals of Fe_1+δTe with nominal compositions of δ = 0, 0.06, 0.12, 0.18, and investigated several physical properties including structural parameters, magnetic susceptibility, and electric resistivity. We have found (i) a reduction of the Te-Fe-Te bond angle, (ii) an increase of the number of local moments, and (iii) a gradual change from metallic to semiconducting behavior in electronic transports with increasing δ.