Modification of exchange bias by cooling field without changing the ferromagnetic magnetization

In this work, cooling fields (HFC) with different signs or magnitudes were applied on ferromagnetic (FM)/antiferromagnetic (AF) films [Pt(10Å)/Co(4Å)]4/NiO(tNiOÅ) when FM magnetization of Pt/Co multilayers was kept in positive saturation state at room temperature. Compared to results at HFC=+5kOe, it is seen that HFC=−1kOe suppressed the exchange bias field (HE) and enhanced the coercivity (HC) at the same time. The phenomenon indicates that AF spins can be modified by cooling field without changing the FM magnetization. The experimental results are understood by the competition between the FM/AF interfacial exchange coupling and Zeeman energy in FM/AF systems with ferromagnetic interfacial coupling. ► Antiferromagnetic (AF) spin configuration is modified only by cooling field. ► Both suppressed exchange bias field (HE) and enhanced coercivity (HC) are achieved at the same time when HFC varies. ► Different cooling fields induce distinct initial non-equilibrium states of AF layer. ► AF domain walls serve as new pinning sites of FM domain walls, leading to the enhancement of HC.