NUCLEAR QUADRUPOLE SPIN-LATTICE RELAXATION IN Bi₄ Ge₃ O₁₂ SINGLE CRYSTALS DOPED WITH ATOMS OF d OR f ELEMENTS. CRYSTAL FIELD EFFECTS IN COMPOUNDS EXHIBITING ANOMALOUS MAGNETIC PROPERTIES
Orlov V.G., Sergeev G.S., Tetsuo Asaji, Kravchenko E.A., Kargin Yu.F.

Received: August 19, 2009

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The nuclear quadrupole spin-lattice relaxation was studied in the range 4.2-300 K for single crystals of Bi₄ Ge₃ O₁₂ doped with minor amounts (the tenth fractions of mol%) of paramagnetic atoms of Cr, Nd, and Gd. Unusual spin dynamic features were recently found for these crystals at room temperature: a dramatic (up to 8-fold) extension of the effective nuclear quadrupole spin-spin relaxation time T^*₂ occurred upon doping the pure Bi₄ Ge₃ O₁₂ sample. Unlike T^*₂, the effective spin-lattice relaxation time T^*₁ at room temperature differs insignificantly for both doped and pure samples. But at lower temperatures, the samples exhibit considerably different behavior of the spin-lattice relaxation with temperature, which is caused by different contributions to the relaxation process of the dopant paramagnetic atoms. The distinctive maximum in the temperature dependence of the spin-lattice relaxation time for the Nd-doped crystal is shown to result from the crystal electric field effects.