Quantum Phase Transition from Superparamagnetic to Quantum Superparamagnetic State in Ultra Small CdSe: Cr2+ Quantum Dots by Pushpendra Kumar, Kedar Singh, JACS, DOI: 10.1021/ja2088426


Despite a long history of success in the synthesis, the origin of magnetism in diluted magnetic semiconductors (DMSs) is yet a controversial issue. Doping, that is, intentional incorporation of impurities into a material, is the crucial means of alteration the electronic, optical and magnetic properties of semiconductors. Cr-based DMSs go halves with the other due to remarkable magnetic and magneto-optic properties, originating from the "sp-d" exchange interaction flanked by the band carriers and localized 3d electrons. In the present investigations, tunneling of superparamagnetic (SP) to quantum-superparamagnetic (QSP) state in ultra small (~ 2.5 nm) Cr-doped CdSe DMS-QDs on applying magnetic field at low temperature (in range 50 K to 2 K) is manifested. The quantum critical behavior or Quantum Phase Transition (QPT) of Cr-doped CdSe QDs is prominently revealed from the electron paramagnetic resonance spectra and magnetization measurements. The fascinating interchange flanked by thermal and quantum fluctuations in the vicinity of a quantum critical summit was evidently realized from the inherited high anisotropic field of QDs. A blocking of QSP state of splintered domains is exposed at much lower temperatures attributing to the quantum splitting of a single domain into multi domains. These results not only help to elucidate the origin of the quantum superparamagnetism in non ferrite systems but also represent an advancement toward the controlled manipulation of high-Tc DMS superparamagnetism using external dopant perturbations.

Pushpendra Kumar, Kedar Singh Journal of the American Chemical Society;  DOI: 10.1021/ja2088426

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