Influence of the Colloidal Environment on the Magnetic Behavior of Cobalt Nanoparticles
Guangjun Cheng, Cindi L. Dennis, Robert D. Shull, Angela R. Hight Walker
The magnetic properties of 10 nm cobalt (Co) nanoparticles in 1,2-dicholorbenenze (DCB) are investigated via a series of magnetization (M) vs. temperature (T) measurements. A rapid rise in magnetization around 250 K during warming and a sudden drop at 240 K during cooling are observed when an unsaturated external magnetic field is applied. Differential scanning calorimetry (DSC) measurements demonstrate that the rapid rise and sudden drop in magnetization are associated with the melting and freezing of the solvent, DCB. Magnetic measurements of these Co nanoparticles in DCB are also used to probe their aging process over a period of 70 days. The saturation magnetization and coercivity of Co nanoparticles in DCB decreases over time. Transmission electron microscopy (TEM) characterizations show the evolution of the size, shape, and crystalline structures of these nanoparticles in DCB.