Switching-on superparamagnetism in Mn/CdSe quantum dots

Journal of the American Chemical Society
Donny MaganaGeoffrey F Strouse

Abstract

Mn ion doping of CdSe and other semimagnetic quantum dot (QDs) alloys has been an area of active speculation for over a decade. We report evidence of Mn(II) doping of CdSe grown from a cubic single source precursor that is superparamagnetic (SPM) with a blocking temperature of 40 K following thermal annealing. Prior to thermal annealing the 4 nm Mn/CdSe (1% Mn) QDs exhibit mainly paramagnetic behavior between 300 and 2 K, with a weak antiferromagnetic exchange. Following thermal annealing of the sample, high-temperature ferromagnetic exchange is observed in the magnetization data with the onset of an SPM phase at 40 K that exhibits a coercivity of 0.1 T at 2 K. The switching-on of SPM behavior is believed to be linked to ion migration with formation of (Se-Mn-Se-Mn-Se-Mn)n centers within the nanocrystal that exhibit coupled magnetic moments. Electron paramagnetic resonance (EPR) provides evidence of two distorted T(d) Mn core sites, a clustered site (dipolar broadened), and a localized Mn site (hyperfine-split). The ratio of the EPR signature for the dipolar broadened site increases following annealing and shows a hysteretic response around the blocking temperature. These observations suggest that thermal annealing results in e...Continue Reading

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Citations

May 25, 2012·Nano Letters·Weiwei ZhengGeoffrey F Strouse
May 24, 2012·ACS Nano·Mani P SinghSusan M Kauzlarich
Jun 26, 2009·Expert Opinion on Drug Delivery·Hui Wang, Xiaoyuan Chen
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Oct 3, 2019·The Journal of Chemical Physics·David ParobekDong Hee Son
Apr 7, 2021·Journal of Fluorescence·Sandeep K VaishanavManmohan L Satnami
Dec 5, 2008·Journal of the American Chemical Society·Derek D LovingoodGeoffrey F Strouse
Oct 28, 2008·Journal of the American Chemical Society·Yongan YangY Charles Cao
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Mar 16, 2007·Journal of the American Chemical Society·Shizhong WangAngelique Y Louie
Mar 12, 2008·Nano Letters·Rémi BeaulacDaniel R Gamelin

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