Size-dependent magnetic properties of PtMn nanoparticles

PtMn nanoparticles have been synthesized by chemical methods. The as-synthesized PtMn nanoparticles show superparamagnetic behavior at room temperature and ferromagnetic behavior at 5 K due to the uncompensated surface spins originating from the finite size effect. Different PtMn sizes were obtained after various temperature annealing processes. The exchange bias and vertical loop shift of PtMn nanoparticles were observed at 5 K in field cooling process and were ascribed to the exchange coupling of ferromagnetic surface spins and the antiferromagnetic core. It was found that the coercivity and exchange bias field were strongly related to the particle size.