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

Magnetic doping of semiconductor nanostructures is pursued for applications in magnetic memory and spin-based electronics. A primary goal is to control interactions between carriers (electrons and holes) and the embedded magnetic atoms. We have demonstrated$^{\ast }$ a tunable magnetic \textit{sp-d} exchange interaction between electron-hole excitations and paramagnetic Mn$^{2+}$ ions using `inverted' core-shell nanocrystals composed of Mn$^{2+}$-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 are tunable in magnitude \textit{and sign}. Effective exciton g-factors are controllably tuned from -200 to +30 at 1.6 K by increasing the CdSe shell thickness, demonstrating that strong quantum confinement and wavefunction engineering in heterostructured nanocrystals can be utilized to manipulate carrier-Mn$^{2+}$ wavefunction overlaps \textit{and} the \textit{sp-d }exchange parameters themselves. $^{\ast }$D. Bussian et al., Nature Materials, \textit{in press}.