Magnetic distributions of iron–(nickel zinc ferrite) nanocomposites from first order reversal curve analysis

Abstract

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)Fe2O4 nanocomposites. The Fe-(Ni0.5Zn0.5)Fe2O4 nanocomposite powders were synthesized using a chemical method involving ferrite precipitation and controlled reduction which resulted in the formation of iron nanoclusters 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 iron nanoclusters, 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 iron nanoclusters 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.