Incorporation of cobalt into ZnO nanoclusters

Abstract

The structural, optical and magnetic properties of nanostructured ZnO films co-doped with cobalt and aluminium have been studied. The nanocrystalline films, with cluster sizes in range 50 - 100 nm, were deposited by pulsed laser ablation in a mixed atmosphere of oxygen and helium. The nanocrystallites have the wurtzite structure and are highly oriented with the c-axis perpendicular to the substrate. Both optical and electron spin resonance (ESR) spectroscopy results show the substitutional incorporation of Co$^{2+}$ ions on the Zn site inside the ZnO nanoclusters. The temperature dependence of the ESR spectra follows Curie law corresponding to a paramagnetic material

Role of defects in ferromagnetism inZn1−xCoxO: A hybrid density-functional study

“…7-9͒ in which Co is substituted for Zn rather than forming clusters. These studies also show that nanocrystalline Zn 1−x Co x O is paramagnetic in this concentration range and at low temperature; 8,9 ferromagnetism was observed only at very low temperature. Another agent must therefore be responsible for promotion of high-T c ferromagnetism in Zn 1−x Co x O.…”

“…Recent magnetic resonance, [27][28][29][30][31][32] carrier mobility, 33 positron annihilation spectroscopy, 34 and first-principles calculations [35][36][37] have given a fuller picture of defect-induced electronic states in ZnO. Magnetic resonance techniques 8,9,38 have been applied to Zn 1−x Co x O and Zn 1−x Mn x O films and nanoclusters. As noted above, these studies 8,9,38,39 as well as x-ray magnetic circular dichroism, 12,39 which probe the local crystal structure about the transition-metal ion, have concluded that the transition-metal ions substitute for a Zn ion.…”

“…Magnetic resonance techniques 8,9,38 have been applied to Zn 1−x Co x O and Zn 1−x Mn x O films and nanoclusters. As noted above, these studies 8,9,38,39 as well as x-ray magnetic circular dichroism, 12,39 which probe the local crystal structure about the transition-metal ion, have concluded that the transition-metal ions substitute for a Zn ion. Epitaxial growth of thin films with ͑110͒ orientation has been achieved, 12 and there is considerable anisotropy of the magnetism in the thin film.…”

Ferromagnetic Ordering at Room Temperature in ZnO:Co Nanoparticles

“…The observed RTFM in hydrogenated samples was attributed either to the appearance of Co clusters [3] or oxygen vacancies [4]. Nanocrystals of ZnO:Co are reported to be paramagnetic [5,6], ferromagnetic [7,8] or superparamagnetic [9]. In the present work, we report the observation and possible explanation of intrinsic RTFM in chemically synthesized nanocrystalline ZnO:Co samples having cobalt concentration ranging from 1 to 10 at%.…”

An X-band Co2+ EPR study of Zn1−Co O (x=0.005–0.1) nanoparticles prepared by chemical hydrolysis methods using diethylene glycol and denaturated alcohol at 5 K

“…Co 2 þ -doped ZnO nanoparticles are prospective DMS candidates, and have been investigated extensively . EPR studies of the Co 2 þ ion in magnetic semiconductors, such as SnO 2 [26], provide information on the magnetic state of this compound, and its behavior under different synthesis conditions [1,[16][17][18][19][20][21][22][23][24][25]. The main conclusions of these investigations are: (i) there are present both localized Co 2 þ ions and ferromagnetically coupled Co 2 þ ions in the host material; (ii) The spin-Hamiltonian (SH) parameters for the Co 2 þ ion are very close to those for Co 2 þ -substituted ZnO crystal, characterized by highspin Co 2 þ ions; (iii) there is exhibited an electron paramagnetic resonance (EPR) signal due to Co 2 þ ions, situated in distorted local environment, characterized by high-spin Co 2 þ ions.…”