Coexistence of different charge states in Ta-doped monoclinicHfO2: Theoretical and experimental approaches

A combination of experiments and ab initio quantum-mechanical calculations has been applied to examine hyperfine interactions in Ta-doped hafnium dioxide. Although the properties of monoclinic HfO₂ have been the subject of several earlier studies, some aspects remain open. In particular, time differential perturbed angular correlation spectroscopy studies using Ta-181 as probe atom revealed the coexistence of two hyperfine interactions in this material but an explanation was only given for the more populated one. Until now, no models have been proposed that explain the second interaction, and it has not yet been associated with a specific crystallographic site. In this work, a detailed study of the different charge states for the impurity-probe atom (Ta) was performed in order to understand the second interaction observed in Ta-doped monoclinic HfO2. The combination of experiments and theory suggests that two different charge states coexist in this compound. Further, ab initio calculations predict that, depending on the impurity charge state, a sizeable magnetic moment can be induced at the probe site. This is confirmed by a new analysis of experimental data