Voltage induced reversible and irreversible change of magnetic coercivity in Co/ZnO heterostructure

In this study, the application of bias voltage to 4-8 nm Co/275 nm ZnO heterostructures changed the magnetic behavior reversibly or irreversibly, depending on the different voltage-induced mechanisms. The magnetic coercivity (H_c) monotonically decreased 20% when the small voltages of 0-8 V were applied. The H_c reduction was symmetric with the voltage polarity, and the reversibility was demonstrated by cyclically switching the bias voltage between 0 and 7 V. While a large voltage up to 40 V was applied to the Co/ZnO junction, the current heating effect became considerable and the Co-oxide was formed, as confirmed by depth-profiling X-ray photoemission spectroscopy analysis. The presence of Co-oxide in the Co films induced the irreversible reduction of the Kerr signal and H_c at room temperature. The considerable H_c enhancement at 130 K also indicates the exchange bias coupling effect from the antiferromagnetic Co-oxide.