First order reversal curve measurements offer a powerful approach to quantify the magnetic property distributions in materials. Here, we have used this approach to quantify magnetic property distributions and understand the nano-scale mechanisms contributing to the magnetic anisotropy of Fe-(Ni0.5Zn0.5)Fe2O4nanocomposites. The Fe-(Ni0.5Zn0.5)Fe2O4nanocompositepowders were synthesized using a chemical method involving ferrite precipitation and controlled reduction which resulted in the formation of ironnanoclusters within the ferrite. Two samples with a ∼65% and ∼6% iron composition, respectively, were studied. Transmission electron microscopy measurements yielded an average particle size of ∼15 nm (∼65% Fe) and ∼60 nm (∼6% Fe). The magnetizations at 7 T for the synthesized nanocomposites (M7T = 58 Am2 kg−1 for the ∼65% Fe sample and 55 Am2 kg−1 for the ∼6% Fe sample) are close to that of the bulk saturation magnetization (∼60 Am2 kg−1) of (Ni0.5Zn0.5)Fe2O4. This is not typical in these ferrite systems, due to poor crystallinity. In our samples, the observed large M7T may result from the presence of the ironnanoclusters, as well as improved crystallinity. However, there is a slope to the magnetization at high fields which has typically been attributed to surface spin canting. This may instead be an indication of reduced crystallinity at the surface of the nanoparticles, especially in the ∼65% Fe sample. Furthermore, a difference in interactions between the ferrite and the ironnanoclusters in the two samples results in different anisotropy distributions, as evidenced by a broad transition to saturation for the first sample, and a much sharper transition for the second sample, and confirmed through first order reversal curve measurements.
Received 06 February 2013Accepted 15 April 2013Published online 03 May 2013
The authors thank Dr. John Bonevich for the EDS measurements and Dr. Lily Giri and Dr. Rose Pesce-Rodriguez for the FTIR and TGA measurements. Partial financial support from U.S. Army Communications-Electronics Research, Development and Engineering Center, Space and Terrestrial Communications Directorate is gratefully acknowledged.
We identify certain commercial equipment, instruments, or materials in this article to specify adequately the experimental procedure. In no case does such identification imply recommendation or endorsement by the National Institute of Standards and Technology, the Army Research Laboratory, or the U.S. Government, nor does it imply that the materials or equipment identified are necessarily the best available for the purpose. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation herein.
Article outline: I. INTRODUCTION II. SYNTHESIS III. CHARACTERIZATION METHODS IV. RESULTS AND DISCUSSIONS V. CONCLUSIONS
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