High-performance colossal permittivity behaviour persists to ultralow temperature in Co+Ta co-doped SnO₂: A spin-defect mediated superstable large electronic moment of defect-dipole

Recently, defect complex coupling in nonmagnetic acceptor-donor co-doped binary metal oxides is found to partially localize the donor electrons with a characteristic defect-dipolar freezing temperature (T_f) above which stable colossal permittivity (>10³) persists. However, apart from a lot of co-doping cases, a clear idea of how to tailor the partial localisation behaviour is remain elusive. Here, based on phenomenological theories, we propose a spin-defect mediated partial localisation of donor electrons where the localisation behaviour can be tailored by the strength of exchange correlation between charge carrier spin and local spin. We found an ultrastable high-performance colossal permittivity behaviour over a broad frequency/temperature range in Co+Ta co-doped SnO₂ with an unprecedentedly low T_f (< 2 K) compared with that reported in doped SnO₂ (> 150 K) and other doped binary metal oxides (> 7 K), pointing to a superstable large electronic moment of defect-dipole. The magnetic interactions between magnetic acceptor Co and donor ion significantly change the dielectric behaviour and magnetic order state, which modify the configurations of defect-dipolar clusters and change the partial localisation behaviour of donor electrons due to the exchange correlation between local spin from Co and charge carrier spin from donor. Despite the promising application potential of the novel dielectrics in cryogenic and aerospace microelectronics, the work advances the dielectric physics and benefit the exploration of novel electronic state in metal oxides and semiconductors via defect-engineering.