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 + and H + ion beam irradiation. Upon increasing temperatures, the saturation magnetization ( M s ) in hysteresis loops exhibits an anomalous increase at a high temperature for the unirradiated and the Ni + -beam-irradiated samples, unlike in H + -beam-irradiated sample. Moreover, the magnetization values at low and high temperatures are more intense after Ni + beam irradiation, whereas after H + beam irradiation those are remarkably suppressed. Hematite ( α -Fe 2 O 3 ) 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 + -beam-irradiated samples, but not in H + -beam-irradiated sample. It is thus revealed that the CI particles undergoing the Morin transition cause the anomalous increase in M s . We may suggest that Ni + ion beam increases uncompensated surface spins on the CI particles resulting in a more steep Morin transition and the intensified M s . Ion-beam irradiation may thus be a good tool for controlling the magnetic properties of CI particles, tailoring our work for future applications.