Charge compensation and magnetic properties in Sr and Cu doped La-Fe perovskites

¹ INSTM R.U. and Department of Engineering, University of Bergamo, Dalmine, BG, I-24044 Italy
² CNR - Istituto di Scienze e Tecnologie Molecolari (ISTM), 20133 Milano, Italy
³ INSTM R.U. Firenze and Department of Chemistry, University of Florence, I-50019 Sesto Fiorentino, Italy
⁴ Center for Neutron Research, NIST, Gaithersburg, MD, USA
⁵ Department of Materials Science and Engineering, University of Maryland, College Park, MD20742-2115, USA
⁶ CEA, Centre de Saclay, Service de Physique de l'Etat Condensé, 91191 Gif-sur-Yvette, France

Abstract

Orthorhombic lanthanum orthoferrites La_0.8Sr_0.2Fe_1-yCu_yO_3-w (y = 0 and 0.10) have been studied using X-rays and neutron powder diffraction (XRPD and NPD), magnetization measurements and ⁵⁷Fe Mössbauer spectroscopy. Rietveld refinements on XRPD and NPD data show that they adopt an orthorhombic ABO₃ perovskite symmetry with La/Sr and Fe/Cu atoms randomly distributed on crystal A and B sites, respectively. The magnetic structure at room temperature is antiferromagnetic, with the Fe/Cu magnetic moments aligned along the a axis. Magnetization curves versus temperature show that the compounds exhibit an overall antiferromagnetic and a weak ferromagnetic behaviour in the range 5-298 K. ⁵⁷Fe Mössbauer spectroscopy measurements indicate that Fe³⁺ and Fe⁵⁺ ions coexist in both compounds, and the relative percentage of Fe⁵⁺ is almost the same at 77 and 170 K, rejecting a charge disproportion mechanism.