Y. Oubaid1,2, V. Balédent1,8, O. Fabelo3, L. Bocher1, C. V. Colin4, S. Chattopadhyay5, E. Elkaim2, M. Verseils2, A. Forget6, D. Colson6, D. Bounoua7, P. Fertey2, P. Foury-Leylekian1
1 Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
2 Synchrotron SOLEIL, L’orme des Merisiers, départementale 128, 91190 Saint-Aubin, France
3 Institut Laue-Langevin, 71 avenue des Martyrs, 38042 Grenoble, France
4 Institut Néel, CNRS UPR 2940, 25 av. des Martyrs, Grenoble, 38042, France
5 UGC-DAE Consortium for Scientific Research, Mumbai Centre, 247C, 2nd Floor, Common Facility Building, BARC Campus, Trombay, Mumbai, 400085, India
6 Université Paris-Saclay, CEA, CNRS, SPEC, Gif-sur-Yvette, 91191, France
7 Université Paris-Saclay, CEA, CNRS, LLB, Gif-sur-Yvette, 91191, France
8 Institut universitaire de France (IUF)
Iron-based compounds constitute a major class of materials hosting unconventional superconductivity. Among them, BaFe2S3 occupies a singular position: this quasi-one-dimensional compound, composed of spin ladders, becomes superconducting under pressure but not upon chemical doping. Understanding its ground state at ambient pressure is therefore a crucial step toward identifying the mechanisms underlying the emergence of superconductivity.
In this work, a comprehensive investigation of the structural and magnetic properties of BaFe2S3 is carried out using single crystal X-ray and neutron diffraction. These complementary techniques provide simultaneous access to atomic positions and magnetic order, with neutron scattering offering a unique sensitivity to magnetic moments.
The results first demonstrate that BaFe2S3 is already non-centrosymmetric at room temperature, in contrast to previous assumptions. An additional structural transition is identified at 130 K, while the structure remains polar down to and within the magnetically ordered phase, thereby endowing the compound with multiferroic character. Neutron diffraction plays a central role in determining the magnetic order that sets in at 95 K. It reveals a stripe-type magnetic structure with an important distinction: the iron magnetic moments are non-collinear and exhibit a tilt of approximately 20o with respect to the direction inferred from powder measurements. This subtle feature, inaccessible without neutron scattering, highlights a delicate competition between magnetic interactions and local anisotropies.
The temperature evolution of both magnetic and nuclear Bragg peaks further shows that the magnetoelastic coupling in BaFe2S3 is unexpectedly weak, in marked contrast to its sister compound BaFe2S3.
By revealing the multiferroic nature of BaFe2S3 and the precise characteristics of its magnetic order, this study provides a new framework for understanding this compound and paves the way for exploring the fate of its properties under pressure.
Figure : (Left) atomic and magnetic structure of BaFe2S3. (a) Temperature dependence of the intensities of one magnetic Bragg reflection (1/2,1/2,1) and two nuclear Bragg reflections associated with the structural transition, measured by neutron diffraction. Solid lines correspond to fits using second-order order-parameter functions. (b–d) Temperature evolution of the lattice parameters a, b, and c, extracted from X-ray powder diffraction using the positions of the (2,0,0), (0,6,0), and (0,0,2) Bragg reflections, respectively. The red and black shaded bands indicate the fitted structural and Neel temperatures obtained in figure (a).
