Magnetic and electric transport properties of LaFe0.5Co0.5O3 perovskite system: effect of annealing temperature

C.A. LOPEZ; J. LOHR; M.E. SALETA; J. CURIALE; R. D. SÁNCHEZ

Barcelona

Conferencia; 20th International Conference on Magnetism; 2015

The perovskite-like compound LaFe0.5Co0.5O3 have attracted significant attention for more than a decade, mainly because of their magnetoelectric and multiferroic properties.[1,2] In this work we present the synthesis, structure, magnetism and electric transport properties of different grain size LaFe0.5Co0.5O3 perovskites.Different compounds have been synthesized by citrate method and then annealed 12 hours at different temperatures (Tanneal) between 600 and 1200 °C. The crystallographic characterization was performed by X-ray powder diffraction, the best Rietveld refinement was obtained with a rhombohedral structure (R3c) at room temperature. Also from the X-ray data, we observe the increase of the grain size increasing Tanneal. The temperature and field dependence of the magnetization evidences a ferrimagnetic transition (TC) around 250 K in all cases. Differences in field cooled cooling, field cooled warming and zero-field cooled magnetization suggest the presence of different magnetic states (Ferri and Antiferro) below TC whose ratio change with temperature. Impedance and DC resistivity were characterized as a function of temperature. The resistivity shows a semiconducting-like or thermally activated behavior. From impedance spectroscopy (IS) characterization, we calculated different complex functions as: impedance (Z*), dielectric modulus (M*), permittivity (ε*); and loss tangent (tan δ). The conduction process is dominated by a long-range mechanism in all samples. This process is related to a single relaxations peak in tan δ plots. However, imaginary part of Z* and M* functions show two different relaxations process, which are linked to the grain and grain boundary effects. From this behavior we found the increase of the grain boundary effect as the Tanneal decreases. On the other hand, we observed a subtle effect of Tanneal on the studied magnetic properties. However, differences on the contact between ceramic grains becomes much more important on the transport properties (IS and DC resistivity). As a final remark, our work shows how the synthesis protocol is a powerful tool in the search of specific properties of these kinds of oxides.(1) Fiebig, M.; Lottermoser, T.; Fröhlich, D.; Goltsev, A. V.; Pisarev, R. V. Observation of Coupled Magnetic and Electric Domains. Nature (London, U.K.) 2002, 419, 818−820.(2) Kimura, T.; Goto, T.; Shintani, H.; Ishizaka, K.; Arima, T.; Tokura, Y. Magnetic Control of Ferroelectric Polarization. Nature (London, U.K.) 2003, 426, 55−58.