Ferromagnetism in cluster free, transition metal doped high k dilute magnetic oxides: Films and nanocrystals

摘要

The structural and magnetic properties of high κ dilute magnetic oxides (DMOs) have been studied in two types of samples: thin films and nanocrystals, including Co doped HfO_2 films, Co doped Y_2O_3 films, Co doped Y_2O_3 nanocrystals, and Mn doped Y_2O_3 nanocrystals. The characterizations were conducted by extended x-ray absorption fine structure, x-ray absorption near edge structure, and superconducting quantum interference device vibrating sample magnetometer. Oxygen vacancies are shown to play a crucial role in ferromagnetic ordering, as defect centers in the bound magnetic polaron model to account for DMOs with medium band gap and low carrier concentration. The observation of room temperature ferromagnetism in tri-valence oxide of Y_2O_3 as well as in tetra-valence oxide of HfO_2 suggests a generic feature of transition metal doped high k oxides as good candidates for DMO. The ability to modulate the magnetic behavior of DMO via oxygen vacancy concentration by means of post anneals can be exploited for potential applications in spintronics.