Monitoring the dielectric properties of Mn-ferrite nanoparticles by controlling crystallite size and applying static magnetic field

Mn-ferrite (MnFe₂O₄) nanoparticles were synthesized by a co-precipitation method. Temperature annealing and ball milling were used to change the crystallite size. X-Ray diffractograms (XRD) con?rmed the single phase spinel structure for all samples and calculations showed that the crystallite size is in the range of 8–33 nm. Transmission electron microscope (TEM) images reveals 17–43 nm particle sizes. The frequency and crystallite size dependence of resistivity ρ_ac, dielectric constant ε' and dielectric loss ε'' of all samples were studied without magnetic field and under a dc magnetic field that ranges from 0.1 T to 0.5 T in both the parallel and perpendicular directions to the applied electric field. For all samples, ρ_ac, ε' and ε'' were found to decrease with increasing the applied electric field frequency. ρ_ac decreases while ε' and ε'' increase with increasing the crystallite size. On the other hand, they have the reverse trend with applied magnetic field. All factors that affect these parameters were discussed to explain their behavior. Interestingly, it was found that the resistivity depends linearly on the applied magnetic field. This enables these samples to be used as magnetic sensors. Finally, the sensor sensitivity was controlled by changing the crystallite size of the samples. This work establishes valid ideas for promising applications in the field of magnetic sensors.