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Published on: October 9, 2012
Quantum phase transition from superparamagnetic to quantum superparamagnetic state in ultrasmall Cd(1-x)Cr(II)(x)Se
Weiwei Zheng1, Pushpendra Kumar, Aaron Washington
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306-4390, USA.
Abstract:
Despite a long history of success in formation of transition-metal-doped quantum dots (QDs), the origin of magnetism in diluted magnetic semiconductors (DMSs) is yet a controversial issue. Cr(II)-doped II-VI DMSs are half-metallic, resulting in high-temperature ferromagnetism. The magnetic properties reflect a strong p-d exchange interaction between the spin-up Cr(II) t(2g) level and the Se 4p. In this study, ultrasmall (~3.1 nm) Cr(II)-doped CdSe DMSQDs are shown to exhibit room-temperature ferromagnetism, as expected from theoretical arguments. Surprisingly, a low-temperature phase transition is observed at 20 K that is believed to reflect the onset of long-range ordering of the single-domain DMSQD.
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