Large exchange bias with remarkable thermostability in an inverted quasi core/shell CoO/γ-Fe2O3 granular system

Abstract

An inverted quasi core/shell CoO/γ-Fe2O3 granular system was synthesized through two-step thermal decomposition of acetylacetonate salt. A large exchange bias (EB) effect with remarkable thermostability was found in this granular system. The EB field revealed a large value about 8 kOe at 5 K. A temperature independent-like plateau feature from 75 to 200 K and a high-blocking temperature of EB about 280 K were observed, indicating a remarkable thermostability of EB. Both horizontal and vertical shifts observed in this system could be tuned by the temperature and the cooling field. The linear relation between EB field and pinned uncompensated spins indicated that the uncompensated spins at the interface between CoO and γ-Fe2O3 played an important role in the observed EB effect.