Structural, optical, and magnetic behavior and the nucleation of a Griffiths-like phase in (Ca,V)-doped ZnO nanoparticles

Abstract

Single-phase (Ca,V) co-doped ZnO nanoparticles (Zn_0.93Ca_0.04V_0.03O, called hereinafter ZCVO) were synthesized via a modified sol–gel method. The hexagonal wurtzite symmetry of the ZnO phase nanostructure, belonging to the P6₃mc space group, has been confirmed through X-ray diffraction examinations using Rietveld refinement. No segregated secondary phases or Ca or/and V-rich clusters were detected. The TEM images clearly show the presence of nanoparticles exhibiting a diverse range of spherical shapes. The effect of co-doping on the optical band gap and crystalline quality was also investigated via photoluminescence (PL), UV–vis, and Raman spectrometers. The M–T curve suggests a tenability of magnetic coupling which was discussed within the context of three competing magnetic phases using the 3D spin wave model and Curie–Weiss law. The lack of saturation of the M–H loop at 10 K suggests the presence of both paramagnetic (PM) and ferromagnetic (FM) phases in ZCVO NPs. The bound magnetic polaron (BMP) model provides a plausible explanation for the observed magnetic phase transition. Moreover, a Griffiths-like phase was observed for the first time, to our knowledge, in co-doped ZnO nanoparticles. This novelty may stem from the interplay between the antiferromagnetic (AFM) and FM interactions of the Ca and V ions, which are acquired by oxygen deficiency.