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

Abstract

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 ($$M_{\text {s}}$$ 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 ($$\alpha $$ α -Fe$$_{2}$$ 2 O$$_{3}$$ 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 $$M_{\text {s}}$$ 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 $$M_{\text {s}}$$ 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.