Magnetic properties of dipolar interacting single-domain particles

Abstract

The remanence and coercivity of an assembly of single-domain ferromagnetic particles are studied using the Monte Carlo simulation technique. The particles have random locations, possess random uniaxial anisotropy, and are coupled through dipolar interactions. The dependence of the magnetic properties on the packing density, the size of the particles, and the temperature are examined systematically. The role of the packing geometry ͑sc, fcc͒ and the sample boundaries are discussed. Dipolar interactions are shown to reduce the coercivity with respect to values for the noninteracting assembly in all cases except for strongly dipolar systems below the percolation threshold. An enhancement of the remanence is found in weakly dipolar systems and is attributed to the macroscopic Lorentz field. The fcc packing of the particles leads to more pronounced ferromagnetic behavior than the sc packing. The sample free boundaries and the corresponding demagnetizing field have a strong effect on the remanence of the assembly while they produce a minor reduction to the coercivity. The results from the simulations are compared with magnetic measurements on frozen ferrofluids and granular metal solids. ͓S0163-1829͑98͒03241-X͔

Nonlinear spin wave magnetization of solution synthesized Ni nanoparticles

“…It is known that the consideration of interparticle interactions, dipolar interactions, leads to slower decay of H C with temperature, low remanence, and retention of ferromagnetic character up to temperatures higher than T B eqv , the blocking temperature of noninteracting particles. [28][29][30] This is because the dipolar interactions introduce additional energy barrier for the rotation of particle magnetic moment and this leads to finite …”

“…The temperature dependence of H C in the present case was found to follow closely an empirical relation of the type given below. [28][29][30] …”

Correlation between tunneling magnetoresistance and magnetization in dipolar-coupled nanoparticle arrays

“…Dipolar interaction effects on the MR have been extensively studied experimentally 32 and theoretically 33 in magnetic granular metals, which typically consist of a random assembly of magnetic nanoparticles in a metallic or insulating matrix. Comparing the present results with those for granular metals we could say that the most interesting difference between these two systems, is that in self-assembled arrays an increase of the field sensitivity to an in-plane fields can be achieved by increasing the surface coverage (…”

Spin wave dynamics in two- and three-dimensional superlattices of nanosized ferromagnetic spheres

“…3,4 It is known that the effect of the dipolar interaction strongly depends on the space geometrical order in nanoparticle superlattices and that it can either enhance or decrease the blocking temperature. 5 In this article we present a theoretical investigation of spin waves ͑SW͒ which propagate through a superlattice that consists of interacting nanoscale spheres. By the application of new technologies it is possible to produce self-assembled two-dimensional ͑2D͒ and three-dimensional ͑3D͒ superlattices with various and well defined long-range translational order and with only small deviations from the average size of nanoparticles.…”