Readout of field induced magnetic anisotropy in a magnetoactive elastomer

TL;DR

This study demonstrates that external magnetic fields induce uniaxial magnetic anisotropy in magnetoactive elastomers, which can be read out after cooling, revealing insights into their magnetoelastic properties and potential for enhanced rigidity.

Contribution

It introduces a method to read out magnetic anisotropy in MAEs via cooling and analyzes the restructuring of filler particles under magnetic fields, highlighting a significant ratio of anisotropy constant to shear modulus.

Findings

Magnetic anisotropy in MAE increases with external magnetic field.

Cooling below 220 K immobilizes filler particles, enabling anisotropy readout.

The anisotropy constant is about twice the shear modulus, indicating strong magnetomechanical coupling.

Abstract

It is shown that in external magnetic fields, a uniaxial magnetic anisotropy comes into being in a magnetoactive elastomer (MAE). The magnitude of the induced uniaxial anisotropy grows with the increasing external magnetic field. The filler particles are immobilized in the matrix if the MAE sample is cooled below 220 K, where the anisotropy can be read out. The cooling of the sample is considered as an alternative methodological approach to the experimental investigation of the magnetized state of MAEs. The appearance of magnetic anisotropy in MAE is associated with restructuring of the filler during magnetization, which leads to an additional effective field felt by the magnetization. It is found that the magnitude of the effective magnetic anisotropy constant of the MAE is approximately two times larger than its effective shear modulus in the absence of magnetic field. It is proposed that the experimentally observed large (about 40) ratio of the magnetic anisotropy constant of the filler to the shear modulus of the matrix deserves attention for the explanation of magnetic and magnetoelastic properties of MAEs. It may lead to additional rigidity of the elastic subsystem increasing the shear modulus of the composite material through the magnetomechanical coupling.