Magnetic Response of Magnetoactive Elastomers with Allowance for Slippage at the Particle‐Matrix Interfaces

Abstract

A new model to describe magnetization of a magnetoactive elastomer (MAE) filled with magnetically hard powder is proposed. The magnetization process is treated as a result of a joint contribution of an assembly of single‐domain particles each of which dwells inside its own elastomer cavity. Magnetization of such a particle is a complex magnetomechanical process that combines intrinsic magnetization reversal and particle mechanical rotation. Possible slippage of the particles, in the course of which they disconnect from the matrix and, on their move, rub against the cavity wall, is explicitly taken into account. The influence of the slippage effect on the macroscopic magnetization of the composite is analyzed by means of computer simulation. Occurrence of asymmetrical magnetization loops of single‐domain particles located in an elastic medium is demonstrated. It is shown that by allowing for the slippage, it becomes possible to explain the experimentally observed anomalously low but non‐zero half‐width (coercivity) of the hysteresis loops of the MAE samples.

Magnetization of magnetoactive elastomers under the assumption of breakable adhesion at the particle/matrix interface

“…Similarly to the results obtained for single-domain particles, 19 only small values ( γ * < 20°) affect the half-width for every κ . In particular, at κ = 0.03 the half-width is larger at small γ * because such a soft matrix deforms easily, and the particle slips during the initial magnetization aligning its net magnetic moment with the field and putting itself in an orientation corresponding to the Stoner–Wohlfarth particle whose anisotropy axis is aligned with the field.…”

“…The accumulated data enables one to estimate the critical field max H Ã 0 at which the particle/matrix adhesion breaks. To do that, for each measurement, parameter A 19 2 that is the difference between the areas of the 2nd and 19th loops normalized by their arithmetic mean, was calculated; this indicator is zero if the loop area does not change, and tends to two if the area of the final loop goes to zero. An example of the A 2 19 dependence on max H 0 for the sample s5 (G = 110 kPa) is given in Fig.…”

“…Proceeding to a non-dimensional form, the torques are scaled by the same coefficient 2KV g that was used for the energy (19):…”

“…Without these two assumptions, the motion of the particle–matrix system under Newton's second law in its rotational form was described for the case of a single domain particle in ref. 19.…”

“…In ref. 19 an attempt has been made to elucidate and describe the hysteretic magnetization curves of the above-described type of MH-MAEs. The model was strongly simplified: the complex magnetic architecture of the NdFeB micron-size particles used in real MH-MAEs was ignored, and the particles were assumed to be single-domain grains.…”