Charge-State Control of Mn²⁺ Spin Relaxation Dynamics in Colloidal n‑Type Zn_1–xMn_xO Nanocrystals

Colloidal diluted magnetic semiconductor (DMS) nanocrystals are model systems for studying spin effects in semiconductor nanostructures with relevance to future spin-based information processing technologies. The introduction of excess delocalized charge carriers into such nanocrystals turns on strong dopant–carrier magnetic exchange interactions, with important consequences for the physical properties of these materials. Here, we use pulsed electron paramagnetic resonance (pEPR) spectroscopy to probe the effects of excess conduction band electrons on the spin dynamics of colloidal Mn²⁺-doped ZnO nanocrystals. Mn²⁺ spin–lattice relaxation is strongly accelerated by the addition of even one conduction band electron per Zn_1–xMn_xO nanocrystal, attributable to the introduction of a new exchange-based Mn²⁺ spin relaxation pathway. A kinetic model is used to describe the enhanced relaxation rates, yielding new insights into the spin dynamics and electronic structures of these materials with potential ramifications for future applications of DMS nanostructures in spin-based technologies.