Three-dimensional hopping conduction triggered by magnetic ordering in the quasi-one-dimensional iron-ladder compounds BaFe2S3 and BaFe2Se3

Because the iron-ladder compounds ${\mathrm{BaFe}}_{2}{X}_{3}$ ($X$ = S or Se) possess highly anisotropic crystal, electronic, and magnetic structures, the order in certain degrees of freedom leads to interesting interplays among them. Here we present a systematic study of the dielectric behavior of ${\mathrm{BaFe}}_{2}{\mathrm{S}}_{3}$ and ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$ along all crystallographic directions revealing the conduction mechanism and its relation to the underlying magnetic ordering. The temperature dependence of the DC conductivity indicates that the antiferromagnetic order is accompanied by a transition in the conduction mechanism from a simple activated behavior above ${T}_{\text{N}}$ to three-dimensional variable range hopping below ${T}_{\text{N}}$. Although the magnetic structures that develop on ${\mathrm{BaFe}}_{2}{\mathrm{S}}_{3}$ and ${\mathrm{BaFe}}_{2}{\mathrm{Se}}_{3}$ are rather different---despite nearly identical crystal structures---we do not find significant difference in the conduction mechanism.