Changes in magnetic properties of magnetite Fe3O4 ceramics induced by high energy heavy ion irradiation

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Study of the change induced by heavy ion irradiation in the magnetic properties of magnetite ceramics Fe3O4 can be important for applications. In this work, we report on the effect of the high electronic excitation induced by lead ions on the magnetic properties of highly densified Fe3O4 ceramics. The physical changes induced by irradiation have been investigated by magnetization measurements and Mössbauer spectroscopy, whereas the damage morphology has been observed by TEM. Variations of the saturation magnetization have shown original behaviour versus fluence: the magnetization starts to decrease at low fluence before recovering its initial value at higher fluence. TEM observations have shown the presence of extended spherical defects in the ion wakes. This damage morphology is very similar to that observed for krypton irradiation of the garnet Y3Fe5O12 at low electronic stopping power, which is characterized by a very small amorphous volume. In agreement with this observation, Mössbauer spectroscopy, recorded below the Verwey transition, has shown the absence of a paramagnetic phase. Moreover, Mössbauer spectra exhibited an irradiation-induced anisotropy of the hyperfine magnetic field which revealed the presence of defect-induced anisotropy. Such a result led us to the hypothesis that magnetic domain walls could be pinned by the extended defects, at least for low fluences.