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

Abstract

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 through growth-controlled 'engineering' of electron and hole wavefunctions in 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(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, 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 used to manipulate carrier-Mn(2+) wavefunction overlap and the sp-d exchange parameters themselves.

Paramagnetic, Near‐Infrared Fluorescent Mn‐Doped PbS Colloidal Nanocrystals

“…This value is much larger than that reported for nanoparticles in organic solution (0.5 emu g −1 for x = 3%). [ 14 ] Unlike Mn-doped II-VI nanocrystals, [ 1,2,7,17 ] the PL emission from the Mn dopants in PbS is either not observed or else is much weaker than the QD PL emission ( Figure 3 a,b): the weak Mn-related PL band is centered at ≈1.9 eV at room temperature, at higher energies relative to the much stronger PL emission wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com of the nanocrystals (see Figure 3 b). Also, while the Mn-related PL band does not change with x , the QD PL emission tends to blueshift with increasing x : for PbS QDs with no Mn, the PL band is centered at E QD = 1.08 eV ( λ = 1150 nm) at T = 295 K; increasing Mn results in a monotonic energy blue-shift of the PL emission up to a value of E QD = 1.40 eV ( λ = 885 nm) at x = 18% (see Figure 3 a).…”

“…[1][2][3] In particular, 3 d transition metal ions (Mn, Co, etc.) with their d -shell electronic confi gurations can imprint a nanocrystal with magnetic properties of relevance for innovative applications ranging from bio-imaging [ 4,5 ] to spintronics.…”

“…with their d -shell electronic confi gurations can imprint a nanocrystal with magnetic properties of relevance for innovative applications ranging from bio-imaging [ 4,5 ] to spintronics. [ 1,5 ] For example, colloidal nanocrystals doped with transition metals could provide versatile contrast agents for multimodal medical imaging, i.e., for contrast-enhanced magnetic resonance imaging (MRI) and confocal microscopy. [ 4 ] To date, a variety of nanoparticles (e.g., Fe 3 O 4 , FePt, MnFe 2 O 4 , and MnO) have been used for enhancedcontrast MRI, [ 5,6 ] but these require functionalization with fl uorescent organic dyes for optical imaging and their solubility in physiological solvents demands modifi cation of the nanocrystal surface.…”

Orbital pathways for Mn2+-carriersp−dexchange in diluted magnetic semiconductor quantum dots

“…12,13,[36][37][38][39][40] Most prominently, a strong quantum-confinement-induced change in the fundamental nature of the conduction-band-electron ( e CB − ) -Mn 2+ exchange (s-d exchange) interaction has been described both theoretically 36,37 and experimentally. 37,[41][42][43][44][45] According to k·p-model descriptions of Mn at finite k vectors. 36,37 This mixing has been proposed to turn on strong antiferromagnetic kinetic s-d exchange coupling that dominates over the weaker ferromagnetic potential s-d exchange coupling in DMS QDs and quantum wells (QWs).…”

Excited-State Dynamics in Colloidal Semiconductor Nanocrystals

“…Doping of bulk materials is a very well developed field, which underpins most of our present technologies, since the properties of materials for lighting, electronic and optoelectronic applications are largely controlled by dopants. In contrast, the precise doping of NCs is still an underdeveloped field, which is however booming and has delivered great successes and many novel materials in recent years [28,[91][92][93][94][95][96][97][98][99][100]. Fig.…”