Large coercivity and small exchange bias in Mn3O4 / MnO nanoparticles

Core/shell structured Mn3O4/MnO nanoparticles were prepared by arc evaporating metallic manganese in air. These nanoparticles show unconventional exchange bias phenomena, in which the Curie temperature of the ferrimagnetic Mn3O4 is lower than the Néel temperature of the antiferromagnetic MnO. The exchange bias field in Mn3O4/MnO nanoparticles is much smaller than that in Mn3O4/Mn nanoparticles, due to the weak interfacial exchange coupling. The coercivity of the Mn3O4 phase in nanoscale is almost three times greater than that of the bulk Mn3O4.