Antiferroquadrupolar Ordering in DyB_<b>2</b>C_<b>2</b>Studied by^<b>161</b>Dy Mössbauer Spectroscopy

Abstract

161 Dy Mössbauer effects were measured on the tetragonal antiferroquadrupolar ordered compound DyB 2 C 2 . In the magnetic phase below T C =15.3 K, the Mössbauer spectra are interpreted well by a single set of hyperfine parameters which gives the Dy magnetic moment of 9.0 µ B . The hyperfine field anomalously decreases below T C as temperature decreases, which can be interpreted as symmetry frustration between antiferromagnetic and antiferroquadrupolar interactions acting on Dy 3+ ions. Reflecting the 4 f electronic state in which two Kramers doublets locate with a low-energy separation, the spectra in the antiferroquadrupolar ordered phase and paramagnetic phase are complicated and cannot be well analyzed by the two-level relaxation model with a single set of hyperfine parameters, although it is supposed that the Dy electronic state is one type.