Correlation of coercivity and microstructure of thin CoFe films

The magnetic and structural properties of sputtered Co50Fe50(CoFe) films we re examined. CoFe films 300 Angstrom thick deposited on Si substrates at ro om temperature showed large coercive fields of 140 Oe. When similar thickne ss films were deposited at 100 degrees C, the coercivity dropped to 90 Oe, and when they were deposited on CoO, the coercivity was reduced to 12 Oe. C ross-sectional imaging with transmission electron microscopy revealed that the CoO underlayer had induced a columnar grain structure in the CoFe, with grain diameters ranging from 50 to 150 Angstrom. CoFe films grown on Si co ntained larger grains of 200-350 Angstrom in diameter with fewer distinct v ertical grain boundaries. Lorentz microscopy showed that domain walls in th e hard CoFe film formed complex, fixed patterns in fields less than the coe rcivity, whereas walls in the CoFe/CoO sample were more conformal and mobil e in response to changing fields. Possible structural origins for the wide variation in coercivity obtained with different substrates, deposition temp erature, and thickness of CoFe films are discussed. (C) 2000 American Insti tute of Physics. [S0021-8979(00)02716-X].