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

Abstract

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)₃·3H₂O, Eu(COOCH₃)₃·6H₂O 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.