Optical Studies of Zero-Field Magnetization of CdMnTe Quantum Dots: Influence of Average Size and Composition of Quantum Dots

TL;DR

This study demonstrates that resonant optical excitation can induce and control magnetization in CdMnTe quantum dots via exciton magnetic polarons, with effects influenced by dot size and Mn concentration, and persists up to 160 K.

Contribution

It reveals how optical excitation induces magnetization in magnetic quantum dots and how size and composition affect this process, advancing understanding of spin dynamics in quantum dots.

Findings

Magnetization is induced by resonant optical excitation of spin-polarized excitons.

Larger quantum dots exhibit weaker photo-induced magnetization.

Lower Mn concentration enhances the photo-induced magnetization.

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.