Fabrication And Investigation Of La_0.7Sr_0.3MnO₃/MFe₂O₄ Magnetic Properties Nanocomposites

Spinel ferrites and perovskite manganites were magnetic materials which were widely applied in varied fields such as magnetic storage, catalysis. The resistance, magnetization,magnetoresistance,metal/insulator transition temperature of composite materials would be changed, when the spinel structure CoFe2O4, NiFe2O4 have been introduced into the manganese oxide. The reasons for these changes were part of the metal ions in spinel replace Mn3+ of perovskite manganites, which reduces or dilute the double exchange between the Mn3+ and Mn4+ ions.In this paper, the advantage of sol-gel method were obtained by comparing the different methods, the traditional sol-gel process were improved and prepared spinel and perovskite nanopowders firstly; The coated nano-composite particles were prepared by the modified sol-gel method with one of the two materials as the core, another material as the shell, and then the morphology and performance of particles were detection with XRD, SEM, TEM, VSM and other equipment.The results as follows:1. The size of nano-particle which were prepared by co-precipitation method and traditional sol-gel method are increased with increasing temperature, and the size of prepared sample particle by latter method is small and uniformity; In the sol-gel process the size of samples which were prepared with nitrate as raw material is smaller than the samples prepared with acetate.2. The perovskite La0.7Sr0.3Mn03 nano nano-particle were prepared by the sol-gel method which adding acrylamide polymer agents and anti-collapse of glucose, the size of nano-particle also increases with the increasing temperature, the particle size uniformity and small and no reunion compared with before improved.3. We prepared the series of La0.7Sr0.3MnO3/MFe2O4 Core/Shell nanoparticles by improved polymer networks sol-gel method with manganites La0.7Sr0.3MnO3 as Core material; Found the resulting particles are spherical, well dispersed and uniform size about 20nm, when the mass ratio of shell and core materials was 2:1,600℃annealing treatment 6h, heating rates were 5℃/min. And with shell materials in the proportion composite increase, the saturation magnetization(MS) of composite particles decreased from 47.9 to 25.2eum/g and the coercivity (HC) increases from 25 to 161Oe at the same time.4. The MFe2O4/La0.7Sr0.3MnO3 (M is Ni, Co, Zn) core/shell structure powders, which were prepared use spinel MFe2O4 as nuclear materials, have high purity, uniformity of particle size, small size, and good dispersion. With the change of nuclear materials, saturation magnetization (MS) and coercivity (HC) level have taken place in different trends and changes. The analysis found that these changes are combined with atoms replace in the core-shell junction.