Static and high frequency magnetic properties of amorphous BiFeO3-CuFe2O4 compounds

The magnetic ordering in amorphous radio-frequency sputtered samples of (1–2x) BiFeO3–x CuFe2O4 with x=0.3 has been studied through magnetization and ferromagnetic resonance (FMR) measurements. Unannealed films sputtered in a mixed oxygen–argon atmosphere show a paramagnetic character at room temperature. In samples annealed in air at high temperatures Ta, one observes a large ferromagnetic moment and a uniaxial anisotropy. Both the room temperature magnetization and anisotropy field increase with Ta until the precipitation of crystalline CuO and Bi2Fe4O9 phases at high temperatures leads to a decrease in the magnetic parameters. The FMR linewidth is found to be dependent on Ta: a rapid increase in the linewidth is seen when crystallization commences. We conclude from low temperature magnetization, Curie temperature, and gyromagnetic ratio data that the ferromagnetic character is due to the formation of ferrimagnetically ordered clusters of copper ferrite.