MAGNETIC PROPERTIES OF COBALT NANOPARTICLES IN A COLLOIDAL SOLUTION

 

Guangjun Chenga, Cindi L. Dennisb, Robert D. Shullb, A.R. Hight-Walkera

 

a Optical Technology Division, Physics Laboratory, NIST, 100 Bureau Drive, Gaithersburg, MD 20899-8443

b Materials Science and Engineering Laboratory, NIST, 100 Bureau Drive, Gaithersburg, MD 20899-8552   

 

               Chemically synthesized magnetic nanoparticles with controllable size and shape have found biological applications in magnetic resonance imaging and cancer treatments. However, these applications require knowledge of how the colloidal environment affects the magnetic properties of the nanoparticles. Here, 9nm cobalt nanoparticles synthesized using thermo-decomposition in 1,2-dicholorbenenze (DCB) are used to study the effects of the colloidal environment on the magnetic behavior of cobalt nanoparticles. The magnetic properties are investigated via hysteresis loops and a series of magnetization (M) vs. temperature (T) measurements. Of particular interest in the M vs. T data is a rapid rise in the magnetization observed around the DCB melting point in the warming-up curve and a sudden drop around DCB freezing point in the cooling curve. The rapid rise magnetization around 250K during the warming-up process is related to the ability of physical rotation of the dipolar chains formed by cobalt nanoparticles, and the heat released by freezing of DCB contributes to the sudden drop in magnetization at 240 K during the cooling process. Further results on fully dried samples suggest that the rapid rise and sudden drop can be used to probe the solvent environment of cobalt nanoparticles. The aging process of these cobalt nanoparticles over two-month period of time in DCB is also studied via M vs. T measurements and transmission electron microscopy (TEM). The aging process could involve the oxidation of these nanoparticles and the redissolution of cobalt nanoparticles. 
 
 

Guangjun Cheng

Mentor: Angela R. Hight Walker

phone: (301) 975-5209

fax: (301) 975-6991

Optical Technology Division (844), Physics Laboratory (PL)

Building 216, Room B223

100 Bureau Drive, Stop 8443

Gaithersburg, MD 20899-8443

email: guangjun.cheng@nist.gov

Sigma Xi member: No

Category: Physics