Electronic and transport properties of Eu-substituted infinite-layer strontium ferrite thin films

We investigated the electronic and carrier transport properties of Eu-substituted infinite-layered SrFeO₂ (Eu:SrFeO₂) epitaxial thin films. X-ray photoemission and absorption spectroscopy measurements revealed that the Fe and Eu ions in the Eu:SrFeO₂ films were essentially divalent and trivalent, respectively, regardless of the Eu ion content. Based on the transport measurements performed at 300 K, the carrier concentration (n_e) and Hall mobility of the Eu:SrFeO₂ (x=0.15) films were found to be 2.5 × 10¹⁹ cm^-3 and 0.94 cm² V^-1 s^-1, respectively. The carrier activation efficiency of Eu³⁺, defined as n_e/n _Eu (where n_Eu is the Eu ion concentration), was as low as ∼0.9%. We speculate that excess oxygen atoms incorporated between FeO ₂ sheets behave as carrier compensators and/or strong scatterers.