铁磁-有机化学键在Fe3O4/有机分子纳米颗粒体系中对自旋注入的影响

Spin injection at the interface of Fe3O4/stearic acid molecule has been investigated in a comparative study of Fe3O4 nanoparticles chemically-bonded with molecules (ChemNPs) and Fe3O4 nanoparticles physically-absorbed with molecules (PhysNPs). The resistance of PhysNPs is two orders of magnitude larger than that of ChemNPs, indicating that the resistance of PhysNPs is dominated by the energy barrier at the Fe3O4-molecule interface. A magnetoresistance of -12% under a field of 5.8 kOe at room temperature is observed in ChemNPs, in sharp contrast to the zero magnetoresistance in PhysNPs, reflecting that the chemical bonding is crucial for spin injection. We attribute this result to the induced magnetic moment in molecules by proximity effect, which is likely the origin of the spin-dependent tunneling through molecules. In addition, the estimated relative large spin polarization of ChemNPs suggests that electronic hybridization at interface and improved oxygen stoichiometry of Fe3O4 surface.