Tunable magnetic exchange interactions in manganese-doped inverted core/shell ZnSe/CdSe nanocrystals

摘要

Magnetic doping of semiconductor nanostructures is actively pursued forapplications in magnetic memory and spin-based electronics. Central to theseefforts is a drive to control the interaction strength between carriers(electrons and holes) and the embedded magnetic atoms. In this respect,colloidal nanocrystal heterostructures provide great flexibility viagrowth-controlled `engineering' of electron and hole wavefunctions withinindividual nanocrystals. Here we demonstrate a widely tunable magnetic sp-dexchange interaction between electron-hole excitations (excitons) andparamagnetic manganese ions using `inverted' core-shell nanocrystals composedof Mn-doped ZnSe cores overcoated with undoped shells of narrower-gap CdSe.Magnetic circular dichroism studies reveal giant Zeeman spin splittings of theband-edge exciton that, surprisingly, are tunable in both magnitude and sign.Effective exciton g-factors are controllably tuned from -200 to +30 solely byincreasing the CdSe shell thickness, demonstrating that strong quantumconfinement and wavefunction engineering in heterostructured nanocrystalmaterials can be utilized to manipulate carrier-Mn wavefunction overlap and thesp-d exchange parameters themselves.