Magnetic properties and electronic structure of LaFeAsO0.85F0.1

Abstract

The magnetic properties of the compound LaFeAsO0.85F0.1 were investigated by measurements of the dc magnetization for different values of the magnetic field H=0.02, 1.0 and 2.0T in the temperature range 4.2–300K. Superconducting behavior was found below 26K, whereas a distinct peculiarity in the low-field dependence of the magnetic susceptibility χ(T) was clearly observed at TM≃135K, which resembles a weak ferromagnetic (FM) response with saturation magnetic moment of about 10−4μB per formula unit at 50K. The transition at TM is presumably not governed by magnetic impurities but rather correlated with the antiferromagnetic (AFM) transition in undoped LaFeAsO at about the same temperature. We suggest that the observed magnetic properties of the LaFeAsO0.85F0.1 sample are due to an interplay of FM and AFM transitions, and are presumably related with an intrinsic feature of a small portion of the undoped LaFeAsO phase inherent in our sample. In order to shed light on the problem of magnetic instability of the LaFeAsO, ab initio DFT calculations of the electronic structure and paramagnetic susceptibility were performed within the local spin density approximation. It is shown that a V-shaped peculiarity in the density of electronic states close to the Fermi level can govern magnetic properties of LaFeAsO with fluorine doping and/or oxygen deficiency.