High‐frequency EPR, ESE, and ENDOR spectroscopy of Co‐ and Mn‐doped ZnO quantum dots

Abstract

Co‐ and Mn‐doped ZnO quantum dots (QDs) with ZnO/Zn(OH)2 core–shell structure were studied using high‐frequency electron paramagnetic resonance (EPR), electron spin echo, and electron‐nuclear double resonance (ENDOR) at low temperature. The shape of the EPR spectrum of cobalt ions was observed to change as a result of Co2+ coupling with optically created shallow donors (SDs). This, along with a shift of SDs line, is a direct demonstration of interaction between the magnetic ion and donor electron in confined system of ZnO QD. ENDOR resonance of the 1H hydrogen nuclei detected by the EPR signal of Co2+ and Mn2+ evidence the hyperfine coupling between these ions, located in the ZnO core, and the protons outside the quantum dot core in the shell.

Spin manipulation and spin-lattice interaction in magnetic colloidal quantum dots

“…At the maximum of the EFS intensity, B 0 = 345 mT (see Supplemental Material, S1 [22] CdTe semiconductor bulk layers [23] for ZnSe/MnSe quantum wells [24] or for nonmagnetic In(Ga)As self-assembled QDs [25]. Our T M values are instead similar to those reported for Mn-doped ZnO colloidal QDs [6,7]. Also, we observe an ESEEM signal superimposed to the Hahn echo decay [ Fig.…”

“…Therefore an understanding of the sources of spin dephasing is necessary to design QDs with long T M . Although spin manipulation has been reported for electron spins confined in lateral [4] and magnetic self-assembled [5] QDs, it still remains largely unexplored in colloidal QDs [6,7]. Nevertheless, significant advances in the synthesis of colloidal QDs have enabled the controlled doping of the QDs with magnetic impurities (e.g., Mn) [7,8], flexibility in manipulating the QD surface and environment [8,9], and implementation of the QDs in hybrid nanocomposite device structures [9].…”

Electron spin coherence near room temperature in magnetic quantum dots

“…The long electron spin dynamics lifetime observed at T = 4.5 K ( T M ~ 8 μs and T 1 ~ 10 ms) and, most importantly, the observation of quantum coherence up to T = 230 K ( T M ~ 1 μs) are unprecedented for Mn ions and very rare amongst transition metal ions. For comparison, phase memory or spin–spin relaxation ( T 2 ) times of Mn spins or confined electrons in other low dimensional systems, such as self-assembled QDs 20 24 25 , layered magnetic semiconductors 21 and quantum wells 22 23 , do not exceed 1 ns, and those for magnetic colloidal QDs in the solid state are <1 μs 7 39 . In addition, we note that T 1 for Mn 0.05% is one order of magnitude longer than that found in self-assembled QDs 15 and diluted magnetic quantum wells 17 40 .…”

A Review of EPR Studies on Magnetization of Nanoparticles of Dilute Magnetic Semiconductors Doped by Transition-Metal Ions

“…Intrinsic defects in dilute magnetic semiconductors determine their electrical and magnetic properties. Investigation of donor and acceptor centers in ZnO nanocrystals by EPR is, therefore, quite important, and many EPR studies have been reported [19,[22][23][24][25][26][27], described briefly as follows. It was found that Li and Na, which are components of commonly used compounds for ZnO nanoparticle synthesis, act as shallow donors, and are located in the core of ZnO nanoparticle [22].…”

“…This technique was successfully applied to Li-and Na-doped ZnO nanocrystals [26]. Coand Mn-doped ZnO colloidal quantum dots are promising classes of diluted magnetic semiconductors, and have been investigated recently [27].…”