Linearity of the direct elastomagnetic effect: evaluation and limits

The direct elastomagnetic effect in composite materials, made of ferromagnetic micro-magnets inside an elastomeric matrix, consists in their relative elastic deformation (10-4-10-3) under the action of an external magnetic field, dependent on the equilibrium between the magneto-mechanical moments and the internal elastic reaction, but independent of the standard magnetostriction. This investigation is focused on the evaluation of the strain linearity with the excitation field in view of the application of these materials for MEMS devices. The studied composite is made of permanently magnetized Sm2Co7 microparticles uniformly dispersed inside a silicone matrix. The field-induced strain is measured using a fiber Bragg grating sensor and, at the same time, theoretically evaluated from the model of the direct elastomagnetic effect. The linearity and reversibility of the material response are experimentally verified up to a threshold value of the magnetic field corresponding to the break in the coupling between the particles' magnetic moments and their body and to the passage from the linear magnetization to the non-linear regime accompanied by irreversible magnetization processes.