Mechanism behind the enhanced ferromagnetic contributions upon Ru Substitution in Ca3Mn2O7 from X-Ray absorption spectroscopies

Subías, Gloria ; Cuartero, Vera (Universidad de Zaragoza) ; Herrero-Martín, Javier ; Lafuerza, Sara ; Saveleva, Viktoriia A. ; Glatzel, Pieter ; Torchio, Raffaella ; Mathon, Olivier ; Blasco, Javier

Resumen: We have studied the local structure and electronic and magnetic properties of hybrid improper ferroelectric Ca3Mn2O7 upon Ru substitution at the Mn site by a combination of atomic-selective X-ray absorption spectroscopies in the soft and hard X-ray energy regimes. Ru substitution enhances the macroscopic ferromagnetic contributions, whose origin is here elucidated. In particular, soft X-ray magnetic circular dichroism (XMCD) data indicate that the spin moments of Mn and Ru are aligned in opposite directions, with the effective magnetic moments of Ru being about 1 order of magnitude smaller than for Mn. The XMCD results also demonstrate the presence of an intrinsic ferromagnetic component in the Mn sublattice for Ru contents x ≥ 0.3, although the values of the net Mn magnetic moment are much smaller than expected for a fully saturated Mn4+ magnetic sublattice. Soft and hard X-ray absorption spectroscopy measurements show that Mn keeps a +4 valence state independently of the Ru content, whereas Ru is in an intermediate valence state, ranging between +4.7 (x ≤ 0.1) and +4.4 (x ≥ 0.7). Analysis of the extended X-ray absorption fine structure (EXAFS) signals at the Mn and Ru K-edges suggests the lack of a complete solid solution in the local structure across the entire range of compositions. These findings disclose the existence of charge transfer between Mn and Ru atoms, so the weak ferromagnetic component is attributed to a canting of the antiferromagnetically ordered Mn4+ spins caused by the oxygen-mediated hybridization between localized Mn4+ 3d and itinerant intermediate valence Ru 4d bands, in analogy to the mechanism proposed for ferromagnetism in ordered doubled perovskites with 3d and 4d/5d transition-metal ions. In the present case, disorder prevents the formation of long-range ferromagnetism.

Idioma: Inglés

DOI: 10.1021/acsomega.4c04334

Año: 2024

Publicado en: ACS OMEGA 9, 40 (2024), 41396-41407
ISSN: 2470-1343

Financiación: info:eu-repo/grantAgreement/ES/DGA-FSE/E12-23R-RASMIA
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PID2021-124734OB-C21
Financiación: info:eu-repo/grantAgreement/ES/MICINN/PID2021-124734OB-C22

Tipo y forma: Artículo (Versión definitiva)

Área (Departamento): Área Cienc.Mater. Ingen.Metal. (Dpto. Ciencia Tecnol.Mater.Fl.)