Exchange bias in ferrimagnetic–antiferromagnetic nanocomposite produced by mechanical attrition

Nanoparticles comprising of magnetite (Fe3O4) core–hematite (α-Fe2O3) shell with mean diameter around 9 nm were synthesized by mechanical grinding. Zero-field-cooled (ZFC) and field-cooled (FC) magnetization and hysteresis loop measurements were carried out over the temperature range 5–300 K. Exchange bias varying from 140 to 10 Oe was observed. This is explained as arising due to ferrimagnetic–antiferromagnetic coupling at the nanointerfaces between the two phases. Analysis of data shows a pronounced increase in the effective anisotropy constant as the milling time is increased.