X-and Q-band electron paramagnetic resonance (EPR) study is reported on the SrTiO 3 single crystals doped with 0.5-at.% MnO. EPR spectra originating from the S = 2 ground state of Mn 3+ ions are shown to belong to the three distinct types of Jahn-Teller centres. The ordering of the oxygen vacancies due to the reduction treatment of the samples and consequent formation of oxygen vacancy associated Mn 3+ centres are explained in terms of the localized charge compensation. The EPR spectra of SrTiO 3 : Mn crystals show the presence of next nearest neighbor exchange coupled Mn 4+ pairs in the <110> directions.

The spin relaxation dynamics of Ce 3+ ions in heavily cerium-doped YAG crystals is studied using pulse-electron paramagnetic resonance and time-resolved pump-probe Faraday rotation. Both techniques address the 4f ground state, while pump-probe Faraday rotation provides also access to the excited 5d state. We measure a millisecond spin-lattice relaxation time T1, a microsecond spin coherence time T2 and a ∼ 10 ns inhomogeneous spin dephasing time T * 2 for the Ce 3+ ground state at low temperatures. The spin-lattice relaxation of Ce 3+ ions is due to modified Raman processes involving the optical phonon mode at ∼ 125 cm −1 . The relaxation at higher temperature goes through a first excited level of the 2 F 5/2 term at about ω ≈ 228 cm −1 . Effects provided by the hyperfine interaction of the Ce 3+ with the 27 Al nuclei are observed.

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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)