[en] Full text: The present work aims at the development of polymer composites with the addition of two types of ferrite particles (magnetite (Fe₃O₄)) for non-destructive evaluation using variation on magnetic field. Glass-polyester composite disks were fabricated with the addition of ferrite particles. Damages were introduced on the disk surfaces and the influences of these damages on the magnetic properties of each material were measured using magnetic flux leakage measurements - MFL. Techniques An X-ray diffraction (XRD) pattern and high-resolution transmission electron microscopy (HRTEM) of the as dried sample clearly indicate the formation of the magnetite phase. The measurements of the magnetic field over the region of the defect indicated a characteristic signature that was directly related to the damage on the disk. These results suggest that the proposed technique has great potential for defect detection in polymer composites. (author)