Magnetic surface effects in ferromagnetic La3Ni2SbO9

FRANCO, D.; CARBONIO, R.; NIEVA, G.

Praga. República Checa.

Conferencia; 9th Conference on Solid State Chemistry; 2010

  Perovskites of general formula ABO3 are very interesting materials because they show a wide variety of physical properties. Substitution at the B site cation gives rise to compounds of general formulae AB1-xB´xO3. If B and B´ are located in two different octahedral crystallographic sites, 2c and 2d, then the material have a double perovskite structure.  In this work we present the double perovskite La3Ni2SbO9 (LaNi2/3Sb1/3O3, x = 1/3). It has been synthesized by solid state method at 1400 ºC in air atmosphere. The Rietveld analysis of the powder diffraction data shows that the structure of the oxide can be well described with the monoclinic space group P 21/n. This space group allows an ordered arrangement of the octahedral ions Ni2+ and Sb5+, but some intrinsic disorder is present due to the stoichiometry. Two different crystallographic sites were found for Ni2+ and Sb5+.  The magnetic properties were measured in a QD magnetometer. c-1 vs. T curves (Fig. 1.a) show a paramagnetic behaviour of Ni2+ down to 176 K, when the system undergoes a ferromagnetic transition. There is also irreversibility between the magnetization measured after cooling in the absence of magnetic field (MZFC) and after cooling in a magnetic field (MFC). The hysteresis loop at 2 K (Fig. 1.b, powder) shows an initial branch that lies outside the hysteresis loop. The same qualitative behaviour is observed at 5, 10 and 15 K. This phenomenology has been reported in nanoparticles [1] where strong surface anisotropy was found. For comparison, in Fig. 1.b we show the hysteresis loop for the pelletized powder, with the initial branch inside the loop. This is in agreement with a surface effect.   [1] R. D. Zysler, D. Fiorani, A. M. Testa, J. Magn. Magn. Materials 224, 5 (2001).