Fe2+ Doping in Antiferromagnetic CsNiCl3 Triggers a Spin Glass Effect, Enhances its Optical and Electrochemical Properties

Room-temperature facile synthesis of CsNiCl₃ is successfully achieved to tune its magnetic, optical, and electrochemical properties by the incorporation of Fe²⁺-ion in the lattice. To ensure phase purity, the synthesized CsNiCl₃ is characterized using powder X-ray diffraction, followed by Rietveld refinement, Fourier transform infrared, Raman spectroscopy, and UV-vis diffuse reflectance measurements. To assess the uniformity of the Fe doping and its oxidation state, field emission scanning electron microscopy mapping and X-ray photoelectron spectroscopy are performed, confirming that Fe²⁺-ions are homogeneously distributed within the lattice. The field and temperature dependent magnetic studies on the doped CsNiCl₃ reveal the presence of spin glass behavior at 52.7 K; the effect can be explained based on intermolecular interaction between nickel and ferrous ions and consequently reduction in spin frustration is observed, in contrast to the magnetic phase transitions observed in the undoped compound at 45.7 and 31.9 K. Moreover, photoluminescence studies indicate the emergence of red emission in CsNi_1−xFe_xCl₃ (x = 0.05, 0.10, and 0.15) with an increase in luminescence lifetime correlating with higher dopant concentration. Electrochemical analysis further reveals that the doped sample enhances ionic conductivity while decreasing diffusional resistance, suggesting potential applications in battery and sensor technologies.