Optical studies of zero-field magnetization of CdMnTe quantum dots: Influence of average size and composition of quantum dots

Abstract

We show that through the resonant optical excitation of spin-polarized excitons into CdMnTe magnetic quantum dots, we can induce a macroscopic magnetization of the Mn impurities. We observe very broad (4 meV linewidth) emission lines of single dots, which are consistent with the formation of strongly confined exciton magnetic polarons. Therefore we attribute the optically induced magnetization of the magnetic dots results to the formation of spin-polarized exciton magnetic polarons. We find that the photo-induced magnetization of magnetic polarons is weaker for larger dots which emit at lower energies within the QD distribution. We also show that the photo-induced magnetization is stronger for quantum dots with lower Mn concentration, which we ascribe to weaker Mn-Mn interaction between the nearest neighbors within the dots. Due to particular stability of the exciton magnetic polarons in QDs, where the localization of the electrons and holes is comparable to the magnetic exchange interaction, this optically induced spin alignment persists to temperatures as high as 160 K.

Magnetic studies on ZnTe:Cr film grown on glass substrate by thermal evaporation method

“…Studies on transition metal doped II-VI compound semiconductors is getting attraction, because transition metals have high solubility in this compound semiconductors than in III-V based compound semiconductors [6]. A lot of fundamental studies have been carried out on transition metal doped II-VI semiconductors such as CdTe [7,8] and ZnTe [9,10]. However, only a little application has been realized and this was because of spin glass or antiferromagnetism in these compound semiconductors [11].…”

Uniform Doping in Quantum-Dots-Based Dilute Magnetic Semiconductor

“…Efforts to understand extended spin interactions in the quantum confined regime has led to the revelation of host of rich physical phenomena including giant Zeeman splitting, 12,13 magnetic polaron 14 and zero field magnetizations. 15 Theory 5,14 and experiments 16 Hence, though delicate engineering of quantum confinement to mediate carrier-spin interactions by altering the size and shape has been recognized as a possibility in solution processed nanocrystals, it has so far been non-trivial to ensure uniform distribution of the dopants in the bulk of the nanocrystals rather than the surface. This is further enhanced by the presence of self-purification mechanisms 18,[25][26][27] in these nanocrystals.…”

Ferromagnetism in transition-metal-doped II–VI compounds

“…The films of them can be grown directly on GaAs substrates. CdMnTe self-assembled quantum dots have been grown [12]. Zn 1Àx M x Te ðM ¼ Cr; MnÞ epitaxial films have been fabricated on GaAs substrates [13].…”