Intrinsic magnetization in the novel quasi-two-dimensional superconducting and magnetic Fe[sub 1+δ]Te[sub 1−x]Se[sub x] system

Intrinsic spin susceptibility of the novel layered superconducting and magnetic system Fe1+δTe1−xSex was investigated by means of the magnetization measurements in comparing with the 125Te NMR Knight shift 125K. The macroscopic uniform susceptibility in Fe1+δTe1−xSex consists of the itinerant magnetization originated in the Fe(1) site, localized one in the Fe(2) site and the ferromagnetic‐like impurity which is frequently sandwiched by the thin film‐like single crystals. Unlike the macroscopic magnetization, Knight shift 125K is mainly attributed to the itinerant magnetism of the Fe(1) site, which is important for the superconductivity and the magnetism in the Fe1+δTe1−xSex system. The magnetic susceptibility estimated in the high‐field region agrees well with 125K. The uniform susceptibility of the superconducting Fe1+δTe1−xSex gradually decreases with decreasing temperature in the normal state accompanied by the growth of antiferromagnetic spin afluctuations.