resumo
Here we report the chemical synthesis of cobalt aluminum oxide (CoAl2O4) nanoparticles by a non-aqueous sol-gel route. The one-pot procedure is carried out at mild temperatures (in the 150 to 300 degrees C range), and consists of the reaction between cobalt acetate and aluminium isopropoxide in benzyl alcohol. The resulting CoAl2O4 nanoparticles show an unusually low average size, between 2.5 and 6.2 nm, which can be controlled by the synthesis temperature. The colorimetric properties of the nanoparticles are also determined by the synthesis temperature and the characteristic blue color of CoAl2O4 pigments is achieved in samples prepared at T >= 200 degrees C. The nanoparticles are antiferromagnetically ordered below similar to 27 K with an uncompensated configuration. The uncompensated moment shows the typical features of strongly interacting superparamagnetic nanoparticles and spin-glass systems.
palavras-chave
SUPERCRITICAL WATER; MEDIATED SYNTHESIS; PIGMENT PARTICLES; COAL2O4; SPINELS; NANOCRYSTALS; ORDER
categoria
Chemistry; Science & Technology - Other Topics; Materials Science; Physics
autores
Karmaoui, M; Silva, NJO; Amaral, VS; Ibarra, A; Millan, A; Palacio, F
nossos autores
Mohamed Karmaoui
Bolseiro de pós-Doutoramento
Nuno João Silva
Investigador Principal
Vitor Brás Sequeira Amaral
Professor CatedráticoProjectos
MULTIFOX: Nanometric Probing and Modification of Multiferroic Oxides (PTDC/FIS/105416/2008)
agradecimentos
The authors thank Dr Walid Hajjaji and Prof. M.F.R. Pereira for granting access to spectrophotometer equipment and Dr P. P. Lima for assistance with the synthesis of organic-inorganic hybrids. M.K. thanks Fundacao para a Ciencia e a Tecnologia (FCT) for grant no. SFRH/BPD/74477/2010. N.J.O.S. thanks FCT for Ciencia 2008 program. Partial funding from FCT under the program COMPETE - FEDER (PTDC/FIS/105416/2008) and Pest-C/CTM/LA0011/2011 is acknowledged. The Aveiro-Zaragoza collaboration has been supported by the Integrated Spanish-Portuguese Action PT2009-0131.