The multiferroic properties of Pb3Fe2F12

Abstract

Fluoride ferroelectrics containing 3d transition metal ions are potential multiferroic candidates due to their ionic bonds rather than the covalent bonds in oxide ferroelectrics. In this work, Pb3Fe2F12 ceramics are prepared by solid-state reaction. Rietveld refinement of the x-ray diffraction pattern suggests that Pb3Fe2F12 adopts a crystalline structure similar to that of Pb5Fe3F19, containing FeF6 octahedra chains and isolated FeF6 octahedra. The deficiency of Pb content leads to the mixed valence states of Fe ions and strong distortion among the octahedra, thus, complicating exchange interactions between Fe ions. The antiferromagnetic transition temperature TN1 is observed at 160 K, which is significantly higher than that of stoichiometric Pb5Fe3F19. Various magnetic anomalies are observed at low temperatures due to the onset of different antiferromagnetic exchange interactions between Fe ions of different strengths with TN2 (∼45 K), TN3 (∼37 K), and TN4 (∼10 K). Weak ferromagnetism can be observed below TN2, and significant exchange bias is observed below TN4. Dielectric peaks, together with a magnetic field tunable pyroelectric current peak, are observed at around TN1, suggesting the multiferroic nature and magnetoelectric coupling in Pb3Fe2F12.