Dipolar interaction and sample shape effects on the hysteresis properties of 2d array of magnetic nanoparticles

Abstract

We study the ground state and magnetic hysteresis properties of 2d arrays (Lx × Ly) of dipolar interacting magnetic nanoparticles (MNPs) by performing micromagnetic simulations. Our primary interest is to understand the effect of sample shape, Θthe ratio of the dipolar strength to the anisotropy strength, and the direction of the applied field ~ H = HoêH on the ground state and the magnetic hysteresis in an array of MNPs. To study the effect of shape of the sample, we have varied the aspect ratio Ar = Ly/Lx which in turn, is found to induce shape anisotropy in the system. Our main observations are: (a) When the dipolar interaction is strong (Θ > 1), the ground state morphology has in-plane ordering of magnetic moments. (b) The ground state morphology has randomly oriented magnetic moments which is robust with respect to system sizes and Ar for weakly interacting MNPs (Θ < 1). (c) Micromagnetic simulations suggests that the dipolar interaction decreases the coercive field Hc. (d) The remanence magnetization Mr is found to be strongly dependent not only on the strength of dipolar interaction but also on the shape of the sample. (e) Due to anisotropic nature of dipolar interaction, a strong effect of shape anisotropy is observed when the field is applied along longer axis of the sample. The dipolar interaction in such a case induces an effective ferromagnetic coupling when the aspect ratio is very large. These results are of vital importance in high-density recording systems, magneto-impedance sensors, etc. ∗ [email protected] 1 ar X iv :2 10 1. 03 35 6v 1 [ co nd -m at .m tr lsc i] 9 J an 2 02 1