1. SYNTHESIS, CHARACTERIZATION AND MAGNETIC PROPERTIES OF La1-xCaxMnO3-δ NANOPARTICLES
M. Vavra1,2, M. Antoňak1, J. Ďurišin3, Marián Mihalik1, Matúš Mihalik4, V. Ocelík5, M. Zentková1
1Institute of Experimental Physics, SAS, Watsonova 47, Košice, Slovakia
2P.J.Šafárik University, Moyzesova 11, Košice, Slovakia
3Institute of Materials Research, SAS, Watsonova 47, Košice, Slovakia
4BENSC – Helmholtz-Zentrum, Glienicker Str. 100, Berlin, Germany
5University of Groningen, Department of Applied Physics, NL-9747 AG Groningen The Netherlands
INTRODUCTION
Recently nanoparticles La0.7Ca0.3MnO3 with the average crystallite size of 10 nm were synthesized for the first time by the glycine–nitrate method without any additional heat treatment. Magnetic measurements shown ferromagnetic transition temperature TC = 120 K [1]. Here we present results of our effort to prepare and study magnetic properties of La1-xCaxMnO3-δ (x = 0.80; 0.33 and 0.15) compounds compromising ferro – magnetic insulator, ferro – magnetic metaal and aniferromagnetic insulator at ambient pressure and high hydrostatic pressure. [1] D. Markovic, V. Kusigerski, M. Tadic et al.: Scr. Mater. 59 (2008)
PREPARATION AND CHARACTERIZATION
Samples were synthesized by the glycine–nitrate method, in which the aqueous solutions of starting constituents in stoichiometric amounts were stirred and heated to dehydrate. Afterwards the solutions became viscous gels which autoignited automatically. After short combustion of only few seconds, black porous ashes of La1-xCaxMnO3-δ were formed. These as-prepared samples were later annealed at 900 °C for 2 h in air to obtain the powders with enlarged size of crystallites. The oxygen content in prepared compounds was estimated by iodometric titration (Tab. 1). Crystal structure was refined from X-ray powder data.
MAGNETIC PROPERTIES UNDER PRESSURE
Heat treatment increases the Curie temperature from 117 K to 147 K. Effect of pressure is different for as prepared sample; TC decreases with pressure. On the other hand the Curie temperature increases with pressure for annealed sample.
Applied pressure does not affect the saturated magnetization of as prepared La0,85Ca0,15MnO2.98 sample, increases remanet magnetization and reduces the coercive force.
Particles of the as prepared La0,85Ca0,15MnO2.98 with the size of about 9 nm and corresponding crystal structure.
Particles of the annealed La0,85Ca0,15MnO2.74 sample with the size between nm and the crystal structure .
X-ray patterns taken at 300 K for as prepared samples and Rietveld refinement
for the annealed sample La0.67Ca0.33MnO2.96
Annealing increases the saturated magnetization. Applied pressure enhanced the saturated magnetization of annealed La0,85Ca0,15MnO2.74 sample, increases remanet magnetization and reduces the coercive force.
Table: Oxygen content, mean oxidation state of Mn atoms (X) and crystal structure lattice parameters.
Sample
Status X δ
a (Ǻ)
b (Ǻ)
c (Ǻ)
V (Ǻ 3)
La0,20Ca0,80MnXO3-δ
prepared
+2,66
0.57 -
La0,67Ca0,33MnXO3-δ
+2,95
0.18
La0,85Ca0,15MnXO3-δ
+3,10
0.02
annealed
+3,80
0.00
+3,41
-0.04
+3,67
-0.26
ACKNOWLEDGEMENT This work is supported by the projects VEGA 2/0057/10 and ERDF EU under the contract No. ITMS