Magnetic field enhanced coercivity of Fe nanoparticles embedded in antiferromagnetic MnN films.

The exchange coupling effect in nanocomposite samples with ferromagnetic (FM) body-centred tetragonal (bct) Fe nanoparticles (NPs) (~20 nm) embedded in an MnN antiferromagnetic (AFM) matrix is investigated. Both the bct Fe NPs control sample and the MnN (×nm)\bct Fe NPs\MnN (20–35 nm)\Ta (5 nm) nanocomposite samples are synthesized by a gas-phase condensation method. Both the coercivity and the remanence ratio of the nanocomposite samples are significantly enhanced compared with the bct Fe NPs sample. The coercivity and the remanence ratio increase with MnN thickness up to 30 nm and then decrease. Additionally, the exchange coupling strength between the bct Fe NPs and AFM MnN matrix is enhanced by magnetic field training. The magnetic field training leads to a higher coercivity and remanence ratio after one cycle of field-cooled hysteresis loop measurement. The coercivity of the composite sample increases by 80%, while the remanence ratio increases by around 30% compared with the bct Fe NPs sample. This work may provide an alternative approach to the design and manufacturing of FM-AFM exchange-coupled permanent magnets. [ABSTRACT FROM AUTHOR]