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

Orthorhombic lanthanum orthoferrites La0.8Sr0.2Fe1-yCuyO3-w (y = 0 and 0.10) have been studied using X-rays and neutron powder diffraction ( XRPD and NPD), magnetization measurements and Fe-57 Mossbauer spectroscopy. Rietveld refinements on XRPD and NPD data show that they adopt an orthorhombic ABO(3) 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. Fe-57 Mossbauer 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.