Local Structure and Room Ferromagnetism of Fe-Doped LiNbO3 Films.

Fe-doped LiNbO₃ thin films were deposited on Si (111) substrates by RF magnetron sputtering technique. The X-ray absorption spectroscopy (XAS) at Fe K-edge revealed the incorporation of Fe ions into Nb sites in the LiNbO₃ host lattice with Fe³⁺ and Fe²⁺ mixed-valent state. The local structural analysis also confirmed that oxygen vacancies are present in the nearest coordination shell of the Fe atoms. The SQUID results showed that all films exhibited room temperature ferromagnetism and the maximum magnetic moment was found when the Fe-doped concentration is 7 at%. The observed room temperature ferromagnetism of Fe-doped LiNbO₃ films could be ascribed to the super-exchange interactions of pentahedral-pentahedral and pentahedral-octahedral Fe³⁺ ions mediated by the oxygen ions, as well as the double-exchange interactions based on the Fe²⁺-O²⁻-Fe³⁺ pairs. Our results demonstrated that the room temperature ferromagnetism can be activated in LiNbO₃ ferroelectrics by introducing transition metal impurities. [ABSTRACT FROM AUTHOR]