Re-entrant spin-glass freezing and magneto-dielectric behaviour of Li3NiRuO5, a layered rock-salt related oxide

We report the results of neutron diffraction, ac and dc magnetization, heat-capacity, complex dielectric permittivity and pyrocurrent measurements on an oxide, Li3NiRuO5, hitherto not paid much attention in the literature, except for a previous report on its promising electrochemical performance. We emphasize on the following findings. (i) Re-entrant spin-glass behaviour is observed; that is, this oxide undergoes ferrimagnetic ordering below 80 K, entering the spin-glass regime around 12 K. (ii) There is no prominent feature in the complex dielectric permittivity (in particular, at the magnetic transitions) in the absence of an external magnetic field, indicative of the absence of ferroelectricity. However, there is distinct evidence for magneto-dielectric (MDE) coupling. The sign of MDE coupling also changes as the sample is cooled from the ferrimagnetic state to the spin-glass regime. (iii) There are pyroelectric anomalies in the vicinity of 30-70 K, presumably arising from thermally stimulated depolarization current.