Identifying the sources of ferromagnetism in sol-gel synthesized Zn1−xCoxO (0≤x≤0.10) nanoparticles

Abstract

We have carefully investigated the structural, optical and electronic properties and related them with changes in the magnetism of sol-gel synthesized Zn 1-x Co x O (0 ≤ x ≤ 0.10) nanoparticles. Samples with x ≤ 0.05 were free of spurious phases. Samples with x ≤ 0.03 were found to be with only high spin Co 2+ ions into ZnO structure, whereas sample with x = 0.05, exhibited the presence of high spin Co 2+ and low spin Co 3+ . We found that the intensity of the main EPR peak associated with Co 2+ varies with the nominal Co content in a similar manner as the saturation magnetization and coercive field do. These results point out that the ferromagnetism in these samples should directly be correlated with the presence of divalent cobalt ions. Bound magnetic polaron (BMP) model and the charge transfer _________________________________________________________________________ 2 model are insufficient to explain the ferromagnetic properties of Zn 1-x Co x O nanoparticles.The room temperature ferromagnetism (RTFM) may be originated from a combination of several factors such as the interaction of high spin Co 2+ ions, perturbation/alteration and/or changes in the electronic structure of ZnO close to the valence band edge and grain boundary effects.

Zero-field magnetic resonance of cobalt ion pairs in ZnO nanocrystals

“…Besides this single-Co 2+ signal, some other weak ESR lines are detected [black marks in Fig. 1(b)], previously seen in several other ESR studies on ZnO:Co NP powder [32][33][34] but not analyzed or assigned to a specific center(s). In the following, these weak ESR lines are investigated and are demonstrated to arise from weakly coupled Co 2+ -Co 2+ pairs with almost isotropic Heisenberg exchange coupling.…”

Local Structure and Surface Properties of CoxZn1–xO Thin Films for Ozone Gas Sensing

“…The lower-energy peak at 530.1 eV (O 1s(1) ) was attributed to the oxygen anions (O 2– ) bound to the metal cations (Zn 2+ or substitutional Co 2+ ) in the tetrahedral sites of the hexagonal wurtzite structure. The second component at approximately 531.2 eV (O 1s(2) ) was assigned to weakly bound −OH species and carbonate species at the sample surface. ,,, Variations in the O 1s(2) component were attributed to differences in the oxygen vacancies or defects at the sample surface or oxygen-deficient regions within the ZnO matrix. , Variation in the oxygen vacancy or defect concentration in the films might facilitate the chemisorption process . The deconvoluted O 1s XPS spectra of the Co x Zn 1– x O samples are shown in Figure S1.…”

“…The second component at approximately 531.2 eV (O 1s(2) ) was assigned to weakly bound −OH species and carbonate species at the sample surface. 30,31,35,36 Variations in the O 1s(2) component were attributed to differences in the oxygen vacancies or defects at the sample surface or oxygendeficient regions within the ZnO matrix. 35,37 Variation in the oxygen vacancy or defect concentration in the films might facilitate the chemisorption process.…”

“…30,31,35,36 Variations in the O 1s(2) component were attributed to differences in the oxygen vacancies or defects at the sample surface or oxygendeficient regions within the ZnO matrix. 35,37 Variation in the oxygen vacancy or defect concentration in the films might facilitate the chemisorption process. 38 The deconvoluted O 1s XPS spectra of the Co x Zn 1−x O samples are shown in Figure S1.…”

Noval properties of PVA/PVP polymer blend doped by nano-ZnO/M (M = Co, Cu, Mn, V)

“…In a tetrahedral environment, the ionic radii of Co 2+ and Zn 2+ are 0.58 and 0.60 Å [37], so it is expected that the lattice parameters tend to decrease slightly with Co 2+ replacing the Zn 2+ in tetrahedral sites in ZnO lattice. The observed increase in the lattice parameters suggests the presence of interstitial Co 2+ and/or Co 3+ ions [38]. Also, the presence of Co 2+ in the high spin state (0.745Ả) would cause an increase in cell parameters [39].…”