An X-band Co²⁺ EPR study of Zn_1-xCo_xO (x=0.005-0.1) nanoparticles prepared by chemical hydrolysis methods using diethylene glycol and denaturated alcohol at 5 K

EPR investigations on two types of dilute magnetic semiconductor (DMS) ZnO nanoparticles doped with 0.5-10% Co²⁺ ions, prepared by two chemical hydrolysis methods, using: (i) diethylene glycol ((CH₂CH₂OH)₂O) (NC-rod-like samples), and (ii) denatured ethanol (CH₃CH₂OH) solutions (QC-spherical samples), were carried out at X-band (9.5 GHz) at 5 K. The analysis of EPR data for NC samples revealed the presence of several types of EPR lines: (i) two types, intense and weak, of high-spin Co²⁺ ions in the samples with Co concentration >0.5%; (ii) surface oxygen vacancies, and (iii) a ferromagnetic resonance (FMR) line. QC samples exhibit an intense FMR line and an EPR line due to high-spin Co²⁺ ions. FMR line is more intense, than the corresponding line exhibited by NC samples. These EPR spectra varied for sample with different doping concentrations. The magnetic states of these samples as revealed by EPR spectra, as well as the origin of ferromagnetism DMS samples are discussed.