Exchange bias of CoO1-δ/(NiFe,Fe) system with blocking temperature beyond Néel temperature of bulk CoO

Abstract

The exchange bias effects in pulsed laser deposited CoO1-δ/(NiFe,Fe) bilayers were investigated. An anomalously high blocking temperature (TB) of 325 K was obtained for the as-deposited CoO1-δ/ferromagnet bilayers, which is 33 K higher than the Néel temperature of the bulk CoO (TN = 292 K). The amount of oxygen vacancies δ in the CoO1-δ film can be controlled by a post-annealing treatment in the O2 atmosphere. The TB of the CoO1-δ/ferromagnet bilayers increases with an increasing δ from δ = 0 to δ = 0.16. Our results indicate that the high TB of CoO1-δ/ferromagnet bilayers originates from the enhancement of the magnetic interaction in the CoO1-δ layer owing to O2- vacancies.