Magnetic anomalies associated with domain wall freezing and coupled electron hopping in magnetite nanorods

Abstract

Magnetite has fascinated researchers for decades, due to its wide range of applications from spintronics to biomedicine. Despite a large body of works aimed at its magnetic properties, no consensus has been reached on the physical origin of the low temperature magnetic anomalies observed in magnetite. Although, a lot of work has been done in studying magnetite nanoparticles, but studies on the low temperature anomalies in those nanoparticles still remains unresearched. We report on the observation of the low temperature magnetic anomalies in highly crystalline, stoichiometric Fe3O4 nanorods and relate them to the coupled electron hopping relaxation process and domain wall motion. Both DC and AC susceptibility show the presence of a hump around 35 K, which is associated with the relaxation of Fe+2 extra electrons. Radio-frequency transverse susceptibility (TS) measurements indicated a noticeable increase in anisotropy field below ~ 25 K, which is attributed to the rearrangement of Fe+2 electrons in the octahedral sites. TS experiments also revealed the domain wall freezing below ~ 35 K. Our combined DC, AC and TS susceptibility studies shed light on the complex nature of the low-temperature magnetic behavior in nanostructured magnetite.