Sputter deposited (CoNi)xO1−x composite materials (abstract)

Abstract

(CoNi) x O 1−x films have been studied extensively for use in high density recording tape media. Fabricated using metal evaporation in a partial pressure of oxygen, these films have exhibited high coercivity with improved corrosion and wear resistance. These attributes appear to be due to the inclined columnar microstructure in which the metal core is surrounded by a magnetic oxide phase. The coercivity could be varied by simply adjusting the atomic ratio of metal to oxide concentration. These properties as well as the possibility of an increased exchange anisotropy field make (Co0.5Ni0.5)xO1−x an interesting material to investigate as a candidate for future high density recording media. We investigated (CoNi)xO1−x composite films using reactive dc magnetron sputtering from a CoNi alloy target in an Ar and O2 environment. The oxide composition of the films was changed by systematically controlling the O2 partial pressure. X-ray diffraction results show that the films consisted of fcc CoNi metal and a fcc oxide phase. The oxide phase consisted of a mixture of NiO, CoO, or CoNiO2. Both the metal and the oxide phase showed a preferential (111) orientation. Calculated using x-ray peak broadening, the crystallite size was observed to decrease from 230 to less than 100 Å with increasing O2 flow rate. Magnetic measurements showed that the saturation magnetization (Ms) decreases from 1000 to 60 emu/cm3 and that the coercivity (Hc) increases from 30 to 300 Oe with increasing O2 flow rate. The easy axis of magnetization appears to be in-plane. Plausible models for the exchanging coupling behavior in composite materials will be discussed.