Structural and magnetic properties of Zn1− x Co x O (0<x⩽0.30) nanoparticles

Abstract: We present a systematic investigation on the structural and magnetic properties of Zn1− x Co x O nanoparticles synthesized by an auto-combustion method. The single-phase Zn1− x Co x O crystallize in the wurtzite-type structure with a homogeneity range as large as x≈0.30, which enables the observation of some anomalies. The lattice parameter a and the unit cell volume V increase with the Co content, and anomalies are discernable around x=0.15 on the a−x and V−x curves. The magnetization data show no evidence of ferromagnetic (FM) ordering in our samples down to T=5K, and the magnetization at 5K and 5T exhibits a maximum around x=0.125. Based on the detailed analysis of the magnetization data and the donor impurity band exchange model, the anomalies on composition dependence of both the lattice parameters and magnetization can be associated with an occurrence of cation percolation around the threshold x p (≈1.5/Z=0.125 for three-dimensional lattice with coordination number Z=12). Within the framework of the donor impurity band exchange model, the absence of FM in the well-characterized Zn1− x Co x O can be attributed to insufficient donor electron concentration. [Copyright &y& Elsevier]