Switching-field and first-order-reversal-curve distribution measurements in magnetic elastomers by molecular dynamics simulations: Accounting for polydispersity.

In this work we employ molecular dynamics simulations to investigate the first-order-reversal-curve distribution and switching-field distribution of magnetic elastomers. We model magnetic elastomers in a bead-spring approximation with permanently magnetized spherical particles of two different sizes. We find that a different fractional composition of particles affects the magnetic properties of elastomers obtained as a result. We prove that the hysteresis of the elastomer can be attributed to the broad energy landscape with multiple shallow minima and caused by dipolar interactions.

Magneto-elastic coupling as a key to microstructural response of magnetic elastomers with flake-like particles.

Using the combination of experiment and molecular dynamics simulations, we investigate structural transformations in magnetic elastomers with NdFeB flake-like particles, caused by applied moderate magnetic fields. We explain why and how those transformations depend on whether or not the samples are initially cured by a short-time exposure to a strong field. We find that in a cured sample, a moderate magnetic field leads mainly to in-place flake rotations that are fully reversed once the applied field is switched off. In contrast, in an initially non-cured sample the flakes perform both translation and rotations under the influence of a moderate applied field that lead to the formation of chain-like structures that remain such even if the field is switched off.

Self-diffusion in bidisperse systems of magnetic nanoparticles.

In the present paper, we study the self-diffusion of aggregating magnetic particles in bidisperse ferrofluids. We employ density functional theory (DFT) and coarse-grained molecular dynamics (MD) simulations to investigate the impact of granulometric composition of the system on the cluster self-diffusion. We find that the presence of small particles leads to the overall increase of the self-diffusion rate of clusters due the change in cluster size and composition.

Importance of matrix inelastic deformations in the initial response of magnetic elastomers.

Being able to predict and understand the behaviour of soft magnetic materials paves the way to their technological applications. In this study we analyse the magnetic response of soft magnetic elastomers (SMEs) with magnetically hard particles. We present experimental evidence of a difference between the first and next magnetisation loops exhibited by these SMEs, which depends non-monotonically on the interplay between the rigidity of the polymer matrix, its mechanical coupling with the particles, and the magnetic interactions in the system. In order to explain the microstructural mechanism behind this behaviour, we used a minimal computer simulation model whose results evidence the importance of irreversible matrix deformations due to both translations and rotations of the particles. To confirm the simulation findings, computed tomography (CT) was used. We conclude that the initial exposure to the field triggers the inelastic matrix relaxation in the SMEs, as particles attempt to reorient. However, once the necessary degree of freedom is achieved, both the rotations and the magnetisation behaviour become stationary. We expect this scenario not only to be limited to the materials studied here, but also to apply to a broader class of hybrid SMEs.