Magnetostructural Transition in Spin Frustrated Halide Double Perovskites

Journal article

Geometrical frustration in the face-centered-cubic (fcc) lattice presents a fundamental challenge in determining antiferromagnetic order, as the ground state is highly sensitive to subtle differences in competing magnetic interactions and structural symmetry. Here, we explore the magnetostructural interplay in two halide double perovskites, Cs2NaFeCl6 and Cs2AgFeCl6. Although both materials have a cubic structure at room temperature, neutron diffraction shows that they adopt different antiferromagnetic structures upon cooling. Cs2NaFeCl6 experiences a transition to an AFM-III order below 2.6 K, governed by J 1 and J 2 (first and second nearest-neighbor) magnetic exchange interactions. Cs2AgFeCl6, however, adopts an AFM-I order below 17 K, accompanied by a significant tetragonal distortion confirmed from both neutron diffraction and polarized Raman spectroscopy. Thermal expansion measurements reveal anomalous lattice expansion at the magnetic transitions in both compounds but are substantially stronger in Cs2AgFeCl6. Combining these findings with density functional theory (DFT) studies, we conclude that the strength of magnetoelastic coupling dictates the magnetic ground state. A strong J 1 in Cs2AgFeCl6 induces a large tetragonal lattice distortion, relieving magnetic frustration and stabilizing the AFM-I phase. In contrast, weaker magnetoelastic coupling in Cs2NaFeCl6 causes minimal distortion, favoring the AFM-III phase via the J 1-J 2 mechanism. Our findings show that magnetic interactions can be a primary driving force for structural phase transitions in these materials, while the strong structural distortion could determine the selection of magnetic ground-state ordering.

Authors: Mopoung, K; Tao, Q; Orlandi, F; Mukhuti, K; Ramsamoedj, KS

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Chemical Society
• Journal: Chemistry of Materials
• Volume: 37
• Issue: 18
• Pages: 6974-6982
• Publication date: 2025-09-08
• Acceptance date: 2025-08-20
• DOI: 10.1021/acs.chemmater.5c00610
• EISSN: 1520-5002
• ISSN: 0897-4756
• Pmid: 41019951
• Language: English