Influence of La substitutions with Sr and Gd in La1-x-ySrxGdyMnO3 perovskite compound on structure and magnetic properties

Abstract

This research reports the studies of crystallographic structure, morphology and magnetic properties of a manganite compound which substitution of Gd and Sr ions at La (or A-site) in the perovskitestructure of La_1-x-ySr_xGd_yMnO₃ (LSGM). While the quantity of Gd and Sr given gives the average size of the cations occupying in A-site or ( 〈 _A 〉 ) is fixed at 1.24 Å for all samples, the significant parameters of Mn⁴⁺ content and the size mismatch of A-site cations ( ²) changed from the substitution of Gd and Sr for La is focused. The LSGM nanopowders are prepared by using the thermal hydro-decomposition method at 900^oC in air for 6 h. The influence of Gd and Sr substitution for La in the sample was characterized by XRD, SEM, TEM and VSM techniques. The XRD result shows that all the prepared samples indexed to a single rhombohedral phase. The morphological investigation of the powder samples from SEM and TEM images reveals the spherical nanoparticles shape with an agglomeration. The average particle sizes of prepared samples are in the range of 28 – 40 nm. The magnetic measurement shows soft ferromagnetic behavior of all samples. The increasing of Mn⁴⁺ contents and ² value (or Gd content) decreases particle size (D), magnetization (M) and Curie temperature (T_C) strongly. A larges ², and an introduction of magnetic layers result in a random arrangement of spin-ordering and also destroy the coupling of Mn³⁺ and Mn⁴⁺ ions in the long-range FM ordering into the short-range magnetically ordered clusters and form spin-cluster glass state.