Ferroelectric And Ferromagnetic Behavior Of Oxide Containing Thin Films

Oxide materials are important due to their interesting physical properties for applications in future electronic devices. Thin film oxide materials show a variety of electric and magnetic properties such as ferroelectric, piezoelectric, ferromagnetic and superconducting properties. One intriguing material, bismuth ferrite, has shown room-temperature multiferroic order. It has ferroelectric order below the 1100 K Curie temperature and large remnant polarization. Also, it has antiferromagnetic order below the Néel temperature of 650 K. However, the bismuth ferrite has several defect-related issues such as bismuth volatilization, transition of iron valence electron states and oxygen vacancies. The multiferroic properties are changed by the defect states of the thin films. In this study, the valence electron transition of iron and oxygen vacancy is investigated. Exchange bias is one of the important phenomena in magnetic materials. The exchange bias is formed from exchange anisotropy between ferromagnetic and antiferromagnetic materials and observed with field-cooling to temperatures lower than the Néel temperature of the antiferromagnetic material. In thin film materials, the phenomenon is also affected by substrate conditions. In this study, the exchange bias is investigated for Co/CoO bilayer thin films on flat substrates and modulated substrates.