High-temperature ferromagnetism of Cu-doped PbPdO2 nanograin films

Abstract

The single-phase, body-centered orthorhombic-structured, Cu-doped PbPdO2 films with a nanograin structure were synthesized by using the sol–gel spin-coating method and an oxidation treatment. It was found that large amounts of Pb vacancies exist in the nanograin film and Pb ions possess a mixed valence state of 2+ and 4+. Besides the superparamagnetism and the charge ordering state, the magnetic studies displayed that ferromagnetism, which can persist up to 380 K, exists in the Cu-doped PbPdO2 nanograin film. As a peculiar characteristic of the spin gapless semiconductor, the ferromagnetic saturation magnetization increasing unusually with temperatures above 300 K was also discovered. The bound magnetic polarons based on the Pb vacancies, the doped Cu2+ ions, and the Pb ions with a valence higher than 2+ were believed to be the origin of such high-temperature ferromagnetism.