Z. Sabsabi, F. Vernay, O. Iglesias, H. Kachkachi
We study the interplay between the effects of surface anisotropy and dipolar interactions in monodisperse assemblies of nanomagnets with oriented anisotropy. We derive asymptotic formulas for the assembly magnetization taking account of the temperature, applied field, core and surface anisotropy, and dipolar inter-particle interactions. We find that the interplay between surface anisotropy and dipolar interactions is well described by the analytical expression of the assembly magnetization that we derive: the overall sign of the product of the two parameters governing the surface and the dipolar contributions determines whether intrinsic and collective terms compete or have a synergistic effect on the magnetization. This is illustrated through a systematic investigation and magnetization curves for monodisperse $\gamma-Fe_{2}O_{3}$ nanoparticles assemblies in the low concentration limit.
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http://arxiv.org/abs/1307.0342
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