Magnetisation distribution in the tetragonal phase of BaFe2As2

TL;DR

This study uses polarized neutron diffraction to map the magnetisation in BaFe2As2's tetragonal phase, revealing it is localized around Fe atoms with a non-spherical distribution indicating 3d t2g orbital involvement.

Contribution

First direct spatial mapping of magnetisation in BaFe2As2's tetragonal phase using maximum entropy reconstruction from polarized neutron data.

Findings

Magnetisation is confined to Fe atoms

Magnetisation distribution is non-spherical

Electrons occupy 3d t2g orbitals, mainly xy symmetry

Abstract

We have determined the spatial distribution of the magnetisation induced by a field of 9 T in the tetragonal phase of BaFe2As2 using polarised neutron diffraction. Magnetic structure factors derived from the polarisation dependence of the intensities of Bragg reflections were used to make a maximum entropy reconstruction of the distribution projected on the 110 plane. The reconstruction shows clearly that the magnetisation is confined to the region around the iron atoms and that there is no significant magnetisation associated with either the As or Ba atoms. The distribution of magnetisation around the Fe atom is significantly non-spherical with a shape which is extended in the <111> directions in the projection. These results show that the electrons which give rise to the paramagnetic susceptibility are confined to the Fe atoms their distribution suggests that they occupy 3d t_2g type orbitals with about 60% in those of xy symmetry.