Magnetic Resonance and Dielectric Studies of a Nonlinear La$\text{}_{3}$Ga$\text{}_{5.5}$Ta$\text{}_{0.5}$O$\text{}_{14}$ Single Crystal Doped with Erbium

Single crystal of erbium doped La$\text{}_{3}$Ga$\text{}_{5.5}$Ta$\text{}_{0.5}$O$\text{}_{14}$ grown by the Czochralski method have been investigated by electron paramagnetic resonance and dielectric spectroscopy methods. Dielectric permittivity ε measurements performed in 90-440 K temperature range have shown negligible dispersion for 1 kHz - 1 MHz frequencies and a Curie-Weiss type behaviour with C=47700 K andθ=-340 K. Electron paramagnetic resonance studies have revealed the presence of two different paramagnetic, monoclinic centres. The calculated g factor values are: g$\text{}_{1}$=1.449, g$\text{}_{2}$=11. 534, g$\text{}_{3}$=4.24 for the main M$\text{}_{1}$ centre and g$\text{}_{1}$=1.98, g$\text{}_{2}$=4.169, g$\text{}_{3}$=4.25 for the weaker M$\text{}_{2}$ centre. The temperature dependence of EPR line intensity for centre M$\text{}_{1}$ and M$\text{}_{2}$ is quite different - while lines attributed to M$\text{}_{1}$ could only be observed at low temperatures, below 20 K, lines of M$\text{}_{2}$ centre persisted up to 200 K. The M$\text{}_{1}$ centre is connected with Er$\text{}^{3+}$ ion entering substitutionally into La$\text{}^{3+}$ site, while M$\text{}_{2}$ is probably connected with 3d ions at the same site, unintentionally introduced into the material as an admixture.