EPR spectroscopy of weak exchange interactions between Co²⁺ ions in ZnO

Abstract

Electron paramagnetic resonance (EPR) is used to identify the next nearest neighbour Co2+ pairs coupled by spin–spin interaction in Co‐doped ZnO single crystals grown by the hydrothermal technique. These dimer centers are described by a spin Hamiltonian with exchange coupling terms written as interaction between identical effective spins Seff = 1/2 of the lowest ground state Kramers doublets of the two Co2+ ions. The exchange parameters of weakly ferromagnetically coupled next nearest neighbor Co2+ pairs are estimated. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photoionization of cobalt impurities in zinc oxide

“…Spectrum of Co 2+ ions (3d 7 configuration) was described by spin Hamiltonian for electron spin S = 3/2: where β is Bohr magneton, g || = 2.24, g ⊥ = 4.554, and A || = 15.9 × 10 −4 cm −1 , A ⊥ = 2.89 × 10 −4 cm −1 are the hyperfine interaction constants of 59 Co isotope (100%) with I = 7/2 . We have not observed Co 2+ ion pairs, as reported in or Cu 2+ ions in ESR spectra.…”

“…Different types of magnetic resonance (MR) signals of ZnCoO were reported in the literature. For samples with a low Co fraction ESR signals of isolated Co 2+ ions and Co–Co pairs were detected, showing the characteristic hyperfine structure of Co . For ZnCoO layers with 10% Co concentration Jedrecy et al observed a broadened and anisotropic paramagnetic signal related to substituting Co 2+ ions.…”

A Review of EPR Studies on Magnetization of Nanoparticles of Dilute Magnetic Semiconductors Doped by Transition-Metal Ions

“…This was explained by invoking the mechanism involving additional defects, e.g. singly charged oxygen vacancies [38]. Another possibility for the existence of ferromagnetically coupled Co 2?…”

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

“…This was explained by invoking the mechanism involving additional defects, e.g. singly charged oxygen vacancies [25]. Another possibility for the existence of ferromagnetically coupled Co 2 þ ions in this nanoparticles was pointed out in [6], where the competition of two Co ions population occurred: one with antiferromagnetic interaction between Co ions and the other with ferromagnetic interaction.…”

“…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.…”