We report experimental studies of a series of $\mathrm{BaF}{\mathrm{e}}_2{\mathrm{S}}_{3-x}\mathrm{S}{\mathrm{e}}_x$ ($0\le x\le 3$) single crystals and powder specimens using x-ray diffraction, neutron-diffraction, muon-spin-relaxation, and electrical transport measurements. A structural transformation from $Cmcm$ ($\mathrm{BaF}{\mathrm{e}}_2{\mathrm{S}}_3$) to $Pnma$ ($\mathrm{BaF}{\mathrm{e}}_2\mathrm{S}{\mathrm{e}}_3$) was identified around $x=0.7-1$. Neutron-diffraction measurements on the samples with $x=0.2$, 0.4, and 0.7 reveal that the Néel temperature of the stripe antiferromagnetic order is gradually suppressed from ∼120 to 85 K, while the magnitude of the ordered $\mathrm{F}{\mathrm{e}}^{2+}$ moments shows very little variation. Similarly, the block antiferromagnetic order in $\mathrm{BaF}{\mathrm{e}}_2\mathrm{S}{\mathrm{e}}_3$ remains robust for $1.5\le x\le 3$ with negligible variation in the ordered moment and a slight decrease of the Néel temperature from 250 K ($x=3$) to 225 K ($x=1.5$). The sample with $x=1$ near the $Cmcm$ and $Pnma$ border shows coexisting, two-dimensional, short-range stripe- and block-type antiferromagnetic correlations. The system remains insulating for all $x$, but the thermal activation gap shows an abrupt increase when traversing the boundary from the $Cmcm$ stripe phase to the $Pnma$ block phase. The results demonstrate that the crystal structure, magnetic order, and electronic properties are strongly coupled in the $\mathrm{BaF}{\mathrm{e}}_2{\mathrm{S}}_{3-x}\mathrm{S}{\mathrm{e}}_x$ system.

• Received 14 April 2020
• Accepted 3 June 2020

DOI:https://doi.org/10.1103/PhysRevB.101.235134