Bulk magnetic measurements and ~(99)Ru and ~(155)Gd Moessbauer spectroscopies of Gd_2Ru_2O_7

摘要

Bulk magnetic measurements and ~(99)Ru and ~(155)Gd Moessbauer effect investigations were performed to examine magnetic properties of the gadolinium pyrochlore ruthenate Gd_2Ru_2O_7. A magnetic transition to the antiferromagnetic state at T_N=114(1) K is accompanied by a small difference between field-cooled and zero-field-cooled magnetic susceptibilities. ~(99)Ru and ~(155)Gd Moessbauer effect investigations at 4.2 K confirmed that both ruthenium and gadolinium sublattices are magnetically ordered. Successful analysis of each spectrum with one set of hyperfine parameters proves that all ruthenium moments have the same magnitude and form the same angle with the local three-fold symmetry axes. The same conclusion concerns Gd magnetic moments. The measured temperature dependence of the hyperfine field at Gd site, together with the molecular-field model, points to the fact that Gd moments also order at T_N, with tiny magnetic moments due to Gd-Ru exchange interaction.