Improper multiferroicity and colossal dielectric constants in Bi${}_2$CuO${}_4$

Abstract

The layered cuprate Bi${}_2$CuO${}_4$ is investigated using magnetic, dielectric and pyroelectric measurements. This system is observed to be an improper multiferroic, with a robust ferroelectric state being established near the magnetic transition. Magnetic and dielectric measurements indicate the presence of a region above the antiferromagnetic Neel temperature with concomitant polar and magnetic short range order. Bi${}_2$CuO${}_4$ is also seen to exhibit colossal dielectric constants at higher temperatures with clearly distinguishable grain and grain boundary contributions, both of which exhibit non-Debye relaxation.