Effect of iron vacancies on the magnetic order and spin dynamics of the spin ladder BaFe$_{2-\delta}$S$_{1.5}$Se$_{1.5}$

TL;DR

This study investigates how approximately 6% iron vacancies affect the magnetic order and spin dynamics in the quasi-one-dimensional spin ladder compound BaFe$_{2-\,delta}$S$_{1.5}$Se$_{1.5}$, revealing suppression of long-range order and coexistence of magnetic correlations.

Contribution

It demonstrates the impact of iron vacancies on magnetic states in a spin ladder system, combining neutron scattering experiments with first-principles calculations to elucidate short-range magnetic orders.

Findings

Long-range magnetic order is absent in the sample.

Both stripe- and block-type antiferromagnetic correlations are observed.

Iron vacancies promote competition between magnetic orders.

Abstract

Quasi-one-dimensional iron chalcogenides possess various magnetic states depending on the lattice distortion, electronic correlations, and presence of defects. We present neutron diffraction and inelastic neutron scattering experiments on the spin ladder compound BaFe$_{2-\delta}$S$_{1.5}$Se$_{1.5}$ with $\sim$6% iron vacancies. The data reveal that long-range magnetic order is absent, while the characteristic magnetic excitations that correspond to both the stripe- and block-type antiferromagnetic correlations are observed. First-principles calculations support the existence of both stripe and block-type antiferromagnetic short-range order in the experimental sample. The disappearance of long-range magnetic order may be due to the competition between these two magnetic orders, which is greatly enhanced for a certain concentration of iron vacancies, which we calculate to be about 6%, consistent with the measured iron vacancy concentration. Our results highlight how iron vacancies in the iron-based spin ladder system strongly influence the magnetic ground state.