ABSTRACT:
There are two common scenarios used to describe the magnetism in Fe-based superconductors.
In one, the magnetism originates from local atomic spins, while in the other it corresponds to a cooperative
spin-density-wave instability (SDW) behavior of conduction electrons. Both assume clear partition into
localized electrons, giving rise to local spins, and itinerant ones, occupying well-defined, rigid conduction
bands. We have used inelastic neutron scattering to characterize both the static and the dynamic magnetism
in a crystal of Fe1.1Te, parent to Fe{1+y}Te{1+x}Se{x} family of superconductors [1]. In contrast to the simple
pictures, we find that localized spins and itinerant electrons are coupled together. In particular, we have
evaluated the effective magnetic moment by integrating both the elastic and inelastic magnetic scattering.
The effective spin per Fe at T = 10 K, in the antiferromagnetic phase, corresponds to S = 1, consistent
with the recent analyses that emphasize importance of Hundâ€™s intra-atomic exchange. However, it grows to
S =3/2 in the disordered phase, a result that presents a challenge to current theoretical models. |