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

Orthorhombic lanthanum orthoferrites La sub(0.8)Sr sub(0.2)Fe sub(1-y)Cu sub(y)0 sub(3.w) (y = 0 and 0.10) have been studied using X-rays and neutron powder diffraction (XRPD and NPD), magnetization measurements and super(57)Fe Mossbauer spectroscopy. Rietveld refinements on XRPD and NPD data show that they adopt an orthorhombic ABO sub(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. super(57)Fe Mossbauer spectroscopy measurements indicate that Fe super(3+) and Fe super(5+) ions coexist in both compounds, and the relative percentage of Fe super(5+) is almost the same at 77 and 170 K, rejecting a charge disproportion mechanism.