A and B-site magnetic contributions in ferrimagnetic ZnFe2O4 thin film and nanoparticles studied using XMCD

C. RODRÍGUEZ TORRES; P. MENDOZA ZÉLIS; G. PASQUEVICH; S. J. STEWART

Workshop; Reunión Anual Usuarios de LNLS; 2013

To investigate the source of magnetism in nanostructured zinc ferrite, we present a study using x-ray absorption (XAS) and magnetic circular dichroism (XMCD) at the L2;3 edges of Fe on zinc ferrite samples of di®erent morphology (¯lms and nanoparticles), all showing a relatively large magnetization at room temperature. The samples consist of: a) a zinc ferrite thin film grown at low O2 pressure, the ¯lm thickness being 57 nm (ZFO1), b) nanostructured ZnFe2O4 particles obtained by mechanically milling hydrothermally prepared nanoparticles (sample 2ZF10H, average grain size D = 13 nm) and c) nanostructured ferrite particles obtained by mechanical grinding bulk ZnFe2O4 (BZF10H, D = 14 nm). In all cases, the x-ray diffraction patterns indicate that all the samples have the spinel structure with cubic symmetry. Our results show that the XMCD signals at room temperature display the typical features observed for ferrites, i.e., a positive peak A1 assigned to magnetic contributions from Fe3+ at tetrahedral A-sites of the spinel structure, and two negative peaks B1 and B2 related to Fe3+ ions at octahedral B-sites. The dichroic signal of ¯lm ZFO1 is markedly higher than those of nanoparticles 2ZF10H and BZF10H. Particularly, XMCD of ZFO1 shows markedly intense B1 and B2 peaks. This fact results in a larger magnetic moment m per iron ion, which is about 40% higher than the m found for nanoparticles. The results are interpreted in terms of differences observed on the distribution of cations, the absence of nonmagnetic ions at B sites added to overpopulation of A sites that took place in ZFO1 ¯lm and the role of oxygen vacancies.