Surface and core magnetic anisotropy in maghemite nanoparticles determined by pressure experiments.

In magnetic nanoparticles, anisotropy energy has extra contributions compared to that of the bulk counterparts, being the most relevant surface anisotropy. Here we use pressure to separate core from surface anisotropy in one system of maghemite nanoparticles dispersed in a polymer. The core anisotropy is K-core=7.7×10(5) erg/cm(3) while the surface anisotropy is K-S=4.2×10(-2) erg/cm(2). This in-one-sample separation is possible due to changes in structurally ordered and disordered ratio, which induce changes in the average magnetic anisotropy energy.