Role of hydroxyl (OH) on structural and ferrimagnetism of annealed CoFe₂O₄ nanoparticles

Abstract

Cobalt ferrites (CoFe₂O₄) with high magnetic moments and coercivity are proposed for the fabrication of media recording devices; however, their very high coercivity, which produces noise, is big hurdle in the practical form of these devices. Cobalt ferrites with high magnetic moment and moderate coercivity, and the role of hydroxyls on the structural and ferrimagnetic properties, have been investigated in detail. The proposed research investigates the following aspects that are important in understanding the role of hydroxyls: (1) the average particle size and presence of hydroxyls are correlated to the annealing temperatures, and (2) the hydroxyls have considerably influenced the structure and magnetic ordering in the nanocrystal. The prepared single spinel structure of cobalt ferrites exhibits good saturated hysteresis loops with ferrimagnetic behaviour and annealing at high temperature observed to play a significant role for the tuning of particle size, saturation magnetisation, coercivity and remnant magnetisation. The removal of hydroxyl at high temperatures in CoFe₂O₄ shows a stable crystallinity with high saturation magnetic moment and moderate coercivity. The novel aspect of the proposed system is the presence of hydroxyls at low annealing temperature, and later, the removal of these hydroxyls at high annealing temperature plays an important role for modifying the magnetic properties. The application of the research can be imagined as applications of media recording devices with low noise and high efficiency and also as antimicrobial/medical applications in biomaterials.

Keywords:

• Hydroxyl
• CoFe₂O₄
• Annealing
• Magnetic nanoparticles
• Ferrimagnetism

This work was supported by the National Natural Science Foundation of China (grant no. 51201037), the Beijing Natural Science Foundation (grant no. 2122020) and China Iron & Steel Research Institute Group Foundation (grant no. SHI11AT0540A) and Advance Technology & Materials Co., Ltd Innovation Foundation (grant no. 2011JA01GYF).