Magnetic and magnetoelastic effects in a composite material of Ni microparticles in a silicone matrix

Ni microparticles in nonmagnetic elastic matrices have a magnetic behavior which depends on particles percentage, temperature, intensity of magnetizing field and the induced strain. In particular, the elastic properties of the matrix give nonconventional effects of deformation on magnetization. When a compression is applied and the magnetizing field is high, i.e., near saturation, it becomes evident the importance of magnetic particles density increment. On the other hand, if the magnetizing field is little, below 1/4 of saturation field, the effect of elastic matrix deformation on particles' orientation and the consequent change of the magnetization intensity is prominent. We named the last peculiar behavior as "elastomagnetic" effect and a simple model to explain it is reported. A threshold field as a function of the particles concentration is experimentally determined which gives the prominence of one or the other of the above described mechanisms. The experimental results and the theoretical model explain that even when the intrinsic magnetoelastic effect is negligible one can find magnetoelastic effects due to coexistence of phases with different geometry, elastic and/or magnetic properties.