Synthesis of Colloidal Mn2+:ZnO Quantum Dots and High-TC Ferromagnetic Nanocrystalline Thin Films

Journal Article · Wed Aug 04 04:00:00 EDT 2004 · Journal of the American Chemical Society, 126(30):9387-9398

DOI:https://doi.org/10.1021/ja048427j· OSTI ID:15020892

Norberg, Nicholas S; Kittilstved, Kevin R; Amonette, James E; Kukkadapu, Ravi K; Schwartz, Dana A; Gamelin, Daniel R

Abstract:We report the synthesis of colloidal Mn2+-doped ZnO (Mn2+:ZnO) quantum dots and the preparation of room-temperature ferromagnetic nanocrystalline thin films. Mn2+:ZnO nanocrystals were prepared by a hydrolysis and condensation reaction in DMSO under atmospheric conditions. Synthesis was monitored by electronic absorption and electron paramagnetic resonance (EPR) spectroscopies. Zn(OAc)2 was found to strongly inhibit oxidation of Mn2+ by O2, allowing the synthesis of Mn2+:ZnO to be performed aerobically. Mn2+ ions were removed from the surfaces of as-prepared nanocrystals using dodecylamine to yield high-quality internally doped Mn2+:ZnO colloids of nearly spherical shape and uniform diameter (6.1 ( 0.7 nm). Simulations of the highly resolved X-and Q-band nanocrystal EPR spectra, combined with quantitative analysis of magnetic susceptibilities, confirmed that the manganese is substitutionally incorporated into the ZnO nanocrystals as Mn2+ with very homogeneous speciation, differing from bulk Mn2+:ZnO only in the magnitude of D-strain. Robust ferromagnetism was observed in spin coated thin films of the nanocrystals, with 300 K saturation moments as large as 1.35 íB/Mn2+ and TC > 350 K. A distinct ferromagnetic resonance signal was observed in the EPR spectra of the ferromagnetic films. The occurrence of ferromagnetism in Mn2+:ZnO and its dependence on synthetic variables are discussed in the context of these and previous theoretical and experimental results.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 15020892
• Report Number(s): PNNL-SA-42140; 2463; KP1704020
• Journal Information: Journal of the American Chemical Society, 126(30):9387-9398, Journal Name: Journal of the American Chemical Society, 126(30):9387-9398 Journal Issue: 30 Vol. 126
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
COLLOIDS
Environmental Molecular Sciences Laboratory
FERROMAGNETISM
HYDROLYSIS
MANGANESE COMPOUNDS
NANOSTRUCTURES
OXIDATION
QUANTUM DOTS
THIN FILMS
ZINC OXIDES
ferromagneticl EPR
quantum dots