Voltage-controlled RKKY Interaction

Magnetic exchange interaction is a quantum effect,which arises from direct over-lap of wave functions or indirect interactions such as superexchange and Ruderman-Kittel-Kasuya-Yosida interaction,whose strength depends closely on the distance be-tween the magnetic atoms and they play vital roles in determining the magnetic prop-erties of nanostructures.Particularly,for the adatoms on the substrate,the exchange interactions between magnetic adatoms on substrates are sensitive to their local envi-ronments.By introducing neighboring adatoms,spin states,magnetic anisotropy,and the Kondo effect of magnetic adatoms can be controlled because of modified exchange interactions between them.In this thesis,we discuss the interaction between the magnetic tip of STM and the Fe adatom on Cu?001?or on a Cu₂N and Cu?001?monolayer surface?Cu₂N/Cu?001??based on the ab initio calculations.A tip-adatom distance-dependent antiferromagnetic-ferromagnetic transition and antiferromagnetic exchange interactions between the tip and the adatom are found for these two junctions,respectively.Based on transport cal-culations,we found that the spin polarization and magnetoresistance in the junction on the Cu?001?system and on the Cu₂N/Cu?001?system depend on the tip-adatom dis-tance.We demonstrate that the different exchange interactions in these systems are determined by the competition between the tip-adatom and the adatom-substrate inter-actions.Such a two-impurity kondo system is essentially composed of the magnetic sys-tem of the impurity at the tip and the adsorption atom respectively and the controllable RKKY interaction between the tip and the adsorption atom.We further studied the modulation of kondo effect by using the distance sensitive dependence on the RKKY interaction between two magnetic atoms.By using the Green's function,we systemati-cally analyze the change of spin exchange interaction with distance,improve the fuzzy region on the phase diagram,and fundamentally discuss the physical mechanism of the change of interaction.Moreover,we compare the results with the ab initio and experi-ments.