Magnetic doping of semiconductor nanostructures is actively pursued for applications in magnetic memory and spin-based electronics. Central to these efforts 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 via growth-controlled `engineering' of electron and hole wavefunctions within individual nanocrystals. Here we demonstrate a widely tunable magnetic sp-d exchange interaction between electron-hole excitations (excitons) and paramagnetic manganese ions using `inverted' core-shell nanocrystals composed of Mn-doped ZnSe cores overcoated with undoped shells of narrower-gap CdSe. Magnetic circular dichroism studies reveal giant Zeeman spin splittings of the band-edge exciton that, surprisingly, are tunable in both magnitude and sign. Effective exciton g-factors are controllably tuned from -200 to +30 solely by increasing the CdSe shell thickness, demonstrating that strong quantum confinement and wavefunction engineering in heterostructured nanocrystal materials can be utilized to manipulate carrier-Mn wavefunction overlap and the sp-d exchange parameters themselves.
@article{arxiv.0811.1036,
title = {Tunable magnetic exchange interactions in manganese-doped inverted core/shell ZnSe/CdSe nanocrystals},
author = {David A. Bussian and Scott A. Crooker and Ming Yin and Marcin Brynda and Alexander L. Efros and Victor I. Klimov},
journal= {arXiv preprint arXiv:0811.1036},
year = {2009}
}
Comments
To appear in Nature Materials; 18 pages, 4 figures + Supp. Info