Stoichiometry Dependence on the Diameter of La2/3Ca1/3MnO3 Manganite Nanoparticles

Abstract

This study presents the magnetic properties of manganite fine particles using Monte Carlo simulations in the framework of a core–shell model. A single-spin movement Metropolis dynamics was implemented to compute equilibrium averages. Calculations were performed on the basis of a three-dimensional classical Heisenberg Hamiltonian, involving the presence of Mn3+ (\(\mathrm{Mn}^{3+e_{g}}\) and \(\mathrm{Mn}^{3+e_{g}'}\)) and Mn4+ (\(\mathrm{Mn}^{4 + d^{3}}\)) cations, and their nearest neighbor interaction. The Hamiltonian includes a surface anisotropy term applied to surface ions, and cubic anisotropy for ions belonging to the core. Different diameters were considered in order to figure out different off-stoichiometric scenarios and the influence on the magnetic properties. Results reveal a well-defined linear particle size inverse dependence of the Curie temperature. No evidence for surface spin disorder was detected. Finally, susceptibility data reveal that the ferromagnetic-to-paramagnetic transition occurs in a gradual fashion ascribed to a differentiated behavior between the core and surface. Initially, the surface contribution to magnetic properties is high; as the nanoparticle size increases, the core contribution becomes stronger.