Magnetic, resonance and transport properties of nanopowder of La0.7Sr0.3MnO3 manganites

X-ray powder diffraction, magnetization, transport and magnetic resonance measurements of nanosize La0.7Sr0.3MnO3 (LCMO) manganites have been performed. The nanosize manganites were synthesized with a co-precipitation method at different (600, 700, 800 and 1000 degrees C) temperatures. The crystal structure of the nanopowders obtained was determined to be perovskite-like with a rhombohedral distortion (the space group R (3) over barc). The average size of synthesized nanoparticles (from 17 to 88 nm) was estimated using the X-ray diffraction and low temperature adsorption of argon methods. All the nanosize manganites show ferromagnetic-like ordering. Both the Curie temperature and magnetization decrease with reducing the particle size. The decrease of magnetization is due to the disordered surface shell of particles. The disordered surface layer is a source of the surface anisotropy and is responsible for the increase of coercivity. Temperature dependences of the magnetic resonance spectra parameters have allowed obtaining information on dynamics of magnetic properties in the nanoparticle systems. The resistivity was established to become higher by reducing the particles' size and increases to a great extent in nanoparticles with the smallest average size at low temperatures. Themagneticentropywas shown to be smaller for the small particles. Using the temperature dependence of magnetic entropy the relative cooling power of the nanosize samples studied was evaluated. (C) 2010 Elsevier B.V. All rights reserved.