Enhanced anomalous magnetization in carbonyl iron by Ni⁺ ion beam irradiation

We investigate the magnetic properties in carbonyl iron (CI) particles before and after Ni[Formula: see text] and H[Formula: see text] ion beam irradiation. Upon increasing temperatures, the saturation magnetization ([Formula: see text]) in hysteresis loops exhibits an anomalous increase at a high temperature for the unirradiated and the Ni[Formula: see text]-beam-irradiated samples, unlike in H[Formula: see text]-beam-irradiated sample. Moreover, the magnetization values at low and high temperatures are more intense after Ni[Formula: see text] beam irradiation, whereas after H[Formula: see text] beam irradiation those are remarkably suppressed. Hematite ([Formula: see text]-Fe[Formula: see text]O[Formula: see text]) phase introduced on the surface of our CI particles undergoes the Morin transition that was observed in our magnetization-temperature curves. The Morin transition causing canted antiferromagnetism above the Morin temperature was found in the unirradiated and Ni[Formula: see text]-beam-irradiated samples, but not in H[Formula: see text]-beam-irradiated sample. It is thus revealed that the CI particles undergoing the Morin transition cause the anomalous increase in [Formula: see text]. We may suggest that Ni[Formula: see text] ion beam increases uncompensated surface spins on the CI particles resulting in a more steep Morin transition and the intensified [Formula: see text]. Ion-beam irradiation may thus be a good tool for controlling the magnetic properties of CI particles, tailoring our work for future applications.