Phase-controlled synthesis and magnetic properties of cubic and hexagonal CoO nanocrystals. (11th October 2016)

• Record Type: Journal Article
• Authors: Qi, Qiongqiong; Chen, Yuanzhi; Wang, Laisen; Zeng, Deqian; Peng, Dong-Liang
• Is Part Of: Nanotechnology. Volume 27:Number 45(2016)
• Publication Date: 2016-10-11
• Subjects: cobalt oxides -- nanocrystals -- solution synthesis -- crystal growth -- magnetic properties; Nanotechnology -- Periodicals; Nanotechnology -- Periodicals; Nanotechnology; Publications périodiques; Nanotechnologies; Periodicals; 620.5
• DOI: 10.1088/0957-4484/27/45/455602
• Languages: English
• ISSNs: 0957-4484

Abstract

Abstract: We report facile solution approaches for the phase-controlled synthesis of rock-salt cubic CoO (c-CoO) and wurtzite-type hexagonal CoO (h-CoO) nanocrystals. In the syntheses, the cobalt precursor cobalt (II) stearate is decomposed in 1-octadecene at 320 °C, and the crystalline phase of synthesized products depend critically on the amounts of H2 O. While the presence of small amounts of H2 O promotes the generation of c-CoO, h-CoO is obtained in the absence of H2 O. The as-prepared c-CoO nanocrystals exhibit a multi-branched morphology with several short rods growing on the 〈100〉 direction interlaced together whereas the h-CoO nanocrystals show a multi-rod structure with several rods growing on the same base facet along the c -axis. The formation mechanisms are discussed on the basis of FTIR spectrometry data and color changes of the reaction mixture. Finally the magnetic properties of as-prepared CoO nanocrystals are measured and the results show that c-CoO nanocrystals are intrinsically antiferromagnetic with a Néel temperature of about 300 K but the antiferromagnetic ordering is not distinct for the h-CoO nanocrystals. Weak ferromagnetic contributions are also observed for both c-CoO and h-CoO nanocrystals with obvious magnetic hysteresis at 5 and 300 K. The uncompensated spins that can be induced by crystalline defects such as cation-vacancy may account for the observed weak ferromagnetism.