161Dy Mössbauer study of DyMn 2Ge 2 - the electronic ground state of the Dy ion, and the magnetic structure

Abstract

The electronic ground state of the Dy ion and the magnetic structure in DyMn 2Ge 2 have been studied by 161Dy Mössbauer spectroscopy. Three different types of spectra are observed corresponding to three magnetic phases. Below 33 K, where the magnetic structure is collinearly ferrimagnetic, the hyperfine parameters derived from the static single-site hyperfine spectra indicate the fact that the electronic ground state of the Dy ion is formed purely with the |− 15 2 〉 state. Above 37.5 K, where the Dy moments remain disordered, the relaxation spectra are observed. From the refined hyperfine parameters, the electronic ground state of the Dy ion is mainly formed with the | ± 15 2 〉 states, and the effect of other states mixed through the crystalline electric field is recognizable. Two hyperfine subspectra for the crystallographically equivalent Dy sites are observed in a temperature range between 33 and 37.5 K, and the intensity ratio between the subspectra is about 1:1, which indicates that there are two kinds of Dy ions with different electronic ground states. From this result, we have deduced a magnetic structure; that is, about 25% abundant ferromagnetic Mn layers couple antiferromagnetically with adjacent ferromagnetic Mn layers, and those Mn layers with antiparallel magnetization distribute randomly along the c axis. The net magnetization of the Mn sublattice aligns antiparallel to that of the Dy sublattice like a ferrimagnetic state.