Monte Carlo simulations of interacting magnetic nanoparticles

Abstract

Motivated by recent advances in synthesis techniques of nanometer size magnetic particles, we have performed Monte Carlo simulations of the magnetic properties of such assemblies of particles. The particles are assumed to be point dipoles, which interact magnetostatically and have uniaxial anisotropy. Spatial distributions of the particles are either generated numerically or are taken from experimental data sets. The properties, such as the remnant magnetization, are studied as a function of temperature for a wide range of parameters. The role of magnetostatic interaction is found to be important in many cases where it has typically been neglected. For example, we find that for a thin film of iron particles with 3.5 nm average diameter and only 13% area coverage, the magnetostatic interactions raise the blocking temperature by 20%, and the particles do not have Stoner–Wolfarth character.

The temperature dependence of hysteretic processes in Co nanowires arrays

“…The equilibrium positions of the polarization vector of the nanowire can be determined by minimizing the energy dE / d =0. 11 Using a Metropolis technique 12,13 for 20ϫ 20 nanowires considered as magnetic dipoles and considering the applied field being parallel with the axis of each nanowires, we obtained the hysteresis loops for the different values of temperatures in the range of 3 -300 K. Figures 3͑a͒ and 3͑b͒ present the hysteresis loops for 3 and 200 K in the case of nanowire having radius R 1 = 0.5 nm, length l = 1000 nm, and a = 3 nm without and with stress term. The shape of hysteresis loops strongly depends on the magnetostatic interaction field H i and thermal stresses.…”

Monte Carlo simulation of magnetic multi-core nanoparticles

“…The second step of the simulation is to calculate the equilibrium magnetization of this cluster by using a Monte Carlo simulation technique. The Monte Carlo methods have proved to be an efficient approach to study the magnetization processes of dipolar-interacting single-domain nanoparticles in thin films [8][9][10].…”

Effect of exchange and dipolar interactions on the hysteresis of magnetic nanoparticle systems

“…The magnetization behavior of single-domain magnetic particles is usually described by the Stoner-Wohlfarth model [5]. Based on the SW model and considering the thermally activated magnetization reversal, two kinds of Monte Carlo methods, local dynamics [6][7][8] and the two-state model [9][10][11][12], are mainly adopted to simulate the magnetic properties of an assembly of nanoparticles. But below the critical temperature the thermal fluctuation around each minimum energy is neglected in the two-state model [10], and the maximum changed region of magnetic moment is not easily chosen in the local dynamics method [13], thus more efforts to simulate the magnetization in the nanoparticle system should be made.…”