Size-dependent spin state and ferromagnetism in La0.8Ca0.2CoO3 nanoparticles

作者：Fita I^*; Markovich V; Wisniewski A; Mogilyansky D; Puzniak R; Iwanowski P; Meshi L; Titelman L; Varyukhin V N; Gorodetsky G

来源：Journal of Applied Physics, 2010, 108(6): 063907.

DOI：10.1063/1.3468463

• ab initio calculations
• electronic structure
• II-VI semiconductors
• nanostructured materials
• polar semiconductors
• semiconductor thin films
• surface reconstruction
• wide band gap semiconductors
• zinc compounds

Magnetic and structural properties of nanocrystalline low-doped La0.8Ca0.2CoO3 cobaltites with particle size of 8, 13, 23, and 50 nm, prepared by the glycine-nitrate method, were investigated in temperature range 5-320 K, magnetic field up to 50 kOe and under hydrostatic pressure up to 10 kbar. With particle downsizing, a noticeable expansion of unit cell, with concomitant changes in the rhombohedral structure toward the cubic one was observed. It was found that the increased surface-disorder effect strongly suppresses the ferromagnetic state in La0.8Ca0.2CoO3 nanoparticles leading to a decrease, by factor of about 2, both in spontaneous magnetization, M-S, and Curie temperature, T-C, when particle's size decreases from 23 to 8 nm. The effective magnetic moment mu(eff) was found also to decrease distinctly due to the strong interdependence between Co-O-Co interactions and Co spin state. The size-induced magnetic disorder drives the La0.8Ca0.2CoO3 nanoparticles to a dominant glassy behavior for 8 nm particles. This is evidenced by the fact that the freezing temperature varies with magnetic field in a strict conformity with the de Almeida-Thouless law for spin glasses and also by the observation of characteristic slowing down in the spin dynamics. The applied pressure suppresses T-C, M-S, and coercive field H-C, like it is observed for bulk La0.8Ca0.2CoO3. Nevertheless, in nanoparticles the pressure effect on T-C is noticeably stronger, while H-C diminishes with pressure much slower then in bulk material.

• 出版日期2010-9-15