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Electron Spin Relaxation of Cu(II) Ions in ZnGeF_6·6H_2O Crystal with Strong Jahn-Teller Effect

100%

Idziak S., Hoffmann S., Goslar J.

Acta Physica Polonica A

2005

vol. 108

issue 1

177-185

Cu^{2+} ions doped to ZnGeF_6·6H_2O substitute the host Zn^{2+} ions and undergo a strong Jahn-Teller effect producing nearly axial elongation of the Cu(H_2O)_6 octahedra with equal population of the three possible deformations at low temperatures as shown by the EPR spectra. Reorientations between these distorted configurations are observed as a continuous shift of EPR lines leading to averaging of the g- and A-tensors. The full averaging is observed at the phase transition temperature 200 K. Electron spin relaxation was measured up to 45 K only, where the electron spin echo signal was detectable. Electron spin-lattice relaxation is governed by the Raman two-phonon process allowing to determine the Debye temperature asΘ_D=99 K. There is no contribution of the Jahn-Teller dynamics to the spin-lattice relaxation rate. Electron spin echo decay is strongly modulated by dipolar coupling to the ^1H and ^{19}F nuclei. The phase memory time is governed by instantaneous diffusion at helium temperatures and then by spin-lattice relaxation processes and excitation to the first vibronic level of energyΔ=151 cm^{-1}.

Influence of the Grain Size on Polaron Transport in Nanostructured La_{2/3}Ca_{1/3}MnO_3 Evidenced by EPR

76%

Raita O., Grecu M., Filip X., Toloman D., Giurgiu L., Idziak S., Hoffmann S.

Acta Physica Polonica A

2005

vol. 108

issue 1

113-118

We report an electron paramagnetic resonance investigation of the grain size effects on the polaron transport in the paramagnetic regime of nanosized La_{2/3} Ca_{1/3}MnO_3 manganites. The temperature dependences of the EPR integral intensity were analyzed in terms of spin-spin exchange interaction and small polaron hopping scenarios. The polaron activation energy decreases with the reduction of the grain size. A discussion is given concerning the factors which could explain the observed change.

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2 Acta Physica Polonica A

2 2005

2 Hoffmann S.

2 Idziak S.

1 Filip X.

1 Giurgiu L.

1 Goslar J.

1 Grecu M.

1 Raita O.

1 Toloman D.

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Electron Spin Relaxation of Cu(II) Ions in ZnGeF_6·6H_2O Crystal with Strong Jahn-Teller Effect

Influence of the Grain Size on Polaron Transport in Nanostructured La_{2/3}Ca_{1/3}MnO_3 Evidenced by EPR