Quantum phase transition from superparamagnetic to quantum superparamagnetic state in In2S3:Eu nanoparticles

Four concentration levels, 0.29 at%, 0.67 at%, 0.99 at% and 1.28 at%, of Eu doped In2S3 nanoparticles (In2S3:Eu) are synthesized by gas-liquid phase chemical deposition using In(COOCH3)(3)center dot 3H(2)O, Eu(COOCH3)(3)center dot 6H(2)O and H2S as the source materials. The structural information of In2S3:Eu is studied by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The photoluminescence (PL) emission spectrum demonstrates that the luminescence quantum efficiency increases upon Eu addition. The magnetic properties using vibrating sample magnetometry (VSM) and Quantum Design MPMS SQUID suggest that Eu doped In2S3 nanoparticles have exhibited the classical thermally driven transition from SP to blocked SP and the quantum phase transition from magnetic long-range order to the QSP state. Calculated spin-resolved density of states (DOS) shows that the origin of the ferromagnetism is primarily due to the Eu atoms. The co-existence of paramagnetism and superparamagnetism have been observed in these doped In2S3 nanoparticles.