AVS 59th Annual International Symposium and Exhibition
    Nanometer-scale Science and Technology Monday Sessions
       Session NS-MoM

Paper NS-MoM9
Magnetic Polymer Nanocomposites with Tunable Microwave and RF Properties

Monday, October 29, 2012, 11:00 am, Room 12

Session: Nanoparticles and Quantum Structures
Presenter: K. Stojak, University of South Florida
Authors: K. Stojak, University of South Florida
S. Chandra, University of South Florida
H. Khurshid, University of South Florida
S. Pal, University of South Florida
C. Morales, University of South Florida
J. Dewdney, University of South Florida
J. Wang, University of South Florida
T. Weller, University of South Florida
M.H. Phan, University of South Florida
H. Srikanth, University of South Florida
Correspondent: Click to Email
There has been much interest in magnetic polymer nanocomposites (MPNCs) recently due to potential applications for EMI shielding, tunable electromagnetic devices and flexible electronics. We report synthesis, structural, magnetic and RF characterization on MPNCs ranging from 30-80wt-% loadings of uniformly dispersed CoFe2O4 nanoparticles (~10nm) in a high-temperature, thermosetting resin from the Rogers Corporation (RP). Nanoparticles were synthesized by thermal decomposition and structurally characterized by XRD and TEM. Magnetic properties were studied using a Quantum Design PPMS. MPNCs displayed characteristic features of superparamagnetism at room temperature and blocking at low temperature. A blocking temperature (TB) of ~298K was observed for all weight percentages. The saturation magnetization (MS) was found to increase with increasing weight percentages of CoFe2O4, from 9.7 emu/g for 30wt-% to 28.5 emu/g for 80wt-%. A large value of coercivity (HC), ~18.5 kOe, is observed at 10K and is not affected by various loadings of CoFe2O4. Microwave transmission/reflection studies were done using a linear microstrip resonator. Strong tunability in the microwave absorption was observed, particularly in the 80wt-% sample and the quality factor shows a strong enhancement with applied magnetic field. We extend our study to include nanoparticle-filled multi-walled carbon nanotubes (CNTs) synthesized by CVD. These high-aspect ratio magnetic nanostructures, with tunable anisotropy, are of particular interest in enhancing magnetic and microwave responses in existing MPNCs. The CNTs have an average diameter and length of 300nm and 2µm, respectively and are partially filled with CoFe2O4 nanoparticles (~7nm) [2]. When comparing the CoFe2O4 nanoparticles to the CoFe2O4-filled CNTs, TB increases from 224K to 264K, and MS increases from 36 emu/g to 37.1 emu/g. These results indicate that enclosing the nanoparticles within the CNTs enhances interparticle interactions, which is also independently confirmed with frequency-dependent AC susceptibility. This trend is also observed with NiFe2O4 and Fe3O4

nanoparticle fillers.