Spin Disorder and Magnetic Anisotropy in Fe3O4 Nanoparticles

Abstract

We have studied the magnetic behavior of dextran-coated magnetite (Fe${}_3$O${}_4$) nanoparticles with median particle size $⟨d⟩=8$ $nm$. Magnetization curves and in-field Mössbauer spectroscopy measurements showed that the magnetic moment $M_S$ of the particles was much smaller than the bulk material. However, we found no evidence of magnetic irreversibility or non-saturating behavior at high fields, usually associated to spin canting. The values of magnetic anisotropy $K_{eff}$ from different techniques indicate that surface or shape contributions are negligible. It is proposed that these particles have bulk-like ferrimagnetic structure with ordered A and B sublattices, but nearly compensated magnetic moments. The dependence of the blocking temperature with frequency and applied fields, $T_B(H,\omega )$, suggests that the observed non-monotonic behavior is governed by the strength of interparticle interactions.

11 pages, 7 figures, 3 Tables

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• Unraveling nanoscale magnetic ordering in Fe3O4 nanoparticle assemblies via x-rays
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