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

Abstract

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

Electrospun nanofiber tubes with elastomagnetic properties for biomedical use

“…At the same time, also the polar attraction among the magnetized particles tries to align them parallel to the magnetizing field axis. These effects into a solid matrix are totally inhibited by the mechanical reaction, but in the case of polymeric fibers that are easily deformable, a local rotation with a fiber aligning towards the tube axis is expected until the elastic reaction torque equilibrates the magnetic one [45]. Generally, any particle has a slight rotation, thus producing an elongation of the sample, namely a direct elastomagnetic effect [50].…”

“…Ni nanoparticles were chosen as filler on the basis of the following points: (i) size ranging from 20 to 100 nm (99,99% Aldrich Chemical) to assure the optimal incorporation in polymer fibers having micrometric diameter; (ii) capability to preserve considerable magnetic moment; (iii) interesting elastomagnetic response when dispersed in a polymer matrix as just reported in previous works [39,45,46]. These requirements are not mandatory for improving biocompatibility [47] or peculiar mechanical properties, but are really important to optimize elastomagnetic response and fiber morphology, preserving magnetization response also in comparison to iron oxides [48].…”

Particle dimension effects on magnetization and strain sensitivity for a composite of nickel particles in silicone matrix

“…In previous papers it was investigated the inverse elastomagnetic effect, namely the reversible change of magnetization due to elastic strain (independent of the intrinsic magnetostriction), which occurs in composite materials of magnetic particles uniformly dispersed in an elastic matrix [1]. The importance of particle preorientation on the magnetization-strain coupling was also already studied [2].…”

Elastomagnetic effect in novel elastic magnets

“…This kind of composite material represents the ideal system for the coupling mechanism between elastic deformation and magnetization that was recently discovered and named elastomagnetic effect [1,2]. In particular, for relative linear deformations up to about 15% the new material exhibits both good elastic characteristics and important magnetoelastic effects not ascribed to intrinsic magnetostriction, but due to the strong coupling between particles rotation and rotation of their permanent magnetic moments.…”