Abstract
Hard/soft CoFe2O4/ZnFe2O4 and soft/hard ZnFe2O4/CoFe2O4 core/shell nanoparticles were prepared by combining high-temperature thermolysis of metal oxide precursors with seed-mediated growth. Magnetic properties of the core/shell nanoparticles were compared to those of individual CoFe2O4 and ZnFe2O4 nanoparticles of similar size prepared by the same method. The structure of the core/shell materials was established using a combination of X-ray and neutron powder diffraction, and transmission electron microscopy. Further evidence for core/shell structure was obtained from magnetic measurements using a SQUID magnetometer. Magnetization measurements as a function of temperature reveal that the core/shell nanoparticles display a single blocking temperature suggesting that the spins of the hard CoFe2O4 and the soft ZnFe2O4 are strongly coupled and respond jointly to changes of temperature and magnetic field. The blocking temperature increases according to the relative amount of hard magnetic material (CoFe2O4) in the nanoparticles in the range of 46-150 K. Magnetic measurements on the nanoparticles as pressed powders and as dispersions in paraffin wax indicate that interparticle interactions significantly influence magnetization and coercivity of the particles, and these must be taken into account before the magnetization behavior of the core/shell structures can be interpreted in terms of coupling between the soft and hard magnetic materials.
| Original language | English |
|---|---|
| Pages (from-to) | 1015-1022 |
| Number of pages | 8 |
| Journal | Solid State Sciences |
| Volume | 8 |
| Issue number | 9 |
| DOIs | |
| State | Published - Sep 2006 |
| Externally published | Yes |
Funding
We acknowledge the donors of the American Chemical Society Petroleum Research Fund for support of this research. The work at UCSB made use of facilities of the Materials Research Laboratory, supported by the National Science Foundation (DMR00 80034). This work has benefited from the use of the Lujan Center at Los Alamos Neutron Science Center, funded by Department of Energy Office of Basic Energy Sciences and Los Alamos National Laboratory funded by Department of Energy under contract W-7405-ENG-36. The upgrade of NPDF has been funded by National Science Foundation through grant DMR00 76488.