Correlation of microstructure and magnetic properties for exchange-biased Co ferromagnets grown above and below the diluted antiferromagnet Co(Mg)O

Abstract

The microstructure of ferromagnetic/antiferromagnetic (FM/AFM) coupled bilayers consisting of 6 nm Co films, grown above and below 20 nm CoO layers diluted with nonmagnetic Mg, is correlated with measurements of exchange-bias field and coercivity as a function of Mg content. Increased Mg dilution is found to slightly decrease the grain width of the columnar oxide layers but no suggestion of Mg segregation at grain boundaries is detected using small-probe microanalysis. The order of growth and the amount of Mg dilution both play an important role in determining the size of the exchange bias field. The large increase in exchange coupling that is measured for Co-below bilayers is attributed to partial oxidation of the upper Co surface during initiation of the AFM deposition. The large decrease in coercivity measured for Co-above bilayers with high Mg dilution is closely correlated with the falloff in exchange-bias field. Overall, these results provide strong support for the uncompensated spin model of exchange bias.