Surface and grain boundary eects on the electric and magnetic properties of La1/2Sr1/2CoO3 nanoparticles.

J. LOHR; M.E. SALETA; J. CURIALE; R.D. SÁNCHEZ

Buenos Aires

Workshop; X-Latin American Workshop on Magnetism and Magnetic Materials and their Applications; 2013

Materia Condensada-CAC-CNEA

The hole-doped La1-xSrxCoO3 compounds present interesting electrical transport and magnetic properties. The undoped LaCoO3 is a charge transfer-type insulator with no magnetic order. The substitution of La3+ by Sr2+ produces a mix valence system with Co3+ and Co4+ which turn on the double exchange mechanism. In this scenario the ferromagnetic correlations and metallic conductivity are promoted. In particular, La1/2Sr1/2CoO3 (LSCO) is a metallic perovskite in thewhole temperature range and it presents ferromagnetic order below 250 K. These properties change abruptly when the grain size is reduced. In this work we present a magnetic and electric comparative study between bulk and nanostructured LSCO. We synthesized LSCO using standard ceramic method (CM) and spray-pyrolysis technique (SP). CM produces bulk samples with grain size at the micron scale, while the SP method has been optimized to obtain a powder of nanocrystals. The powder was pressed and thermally treated at 1073 K under O2 atmosphere during 90 minutes, after that, the sample morphology was studied by scanning electron microscopy (SEM). The micrographs show that the mean size diameter of the nanograins is approximately 15-20 nm. On the other hand, the magnetic activation volume (vac) and the character of the magnetic interactions between grains were obtained from magnetic relaxation, isothermal remanent magnetization (IRM) and dc-demagnetization (DCD) experiments. The diameter obtained from vac is close to the SEM nanograin size. We also determined that the character of the interactions between grains is mainly dipolar. Dierent experiments, as electrical resistivity as a function of temperature and magnetic eld, I-V curves and impedance spectroscopy were performed in order to obtain information about the physics of the interfaces.