Cooling field dependence of exchange anisetropy Was investigated in ferromagnetic(FM)/antiferromagnetic(AFM) bilayers with antiferromngnetle interface coupling. It shows that the exchange bias H_E Can change from negative to positive with increasing cooling field H_CF and cooreivity H_C acquires a maximum near crossover of H_E.Especially.effect of FM and AFM thickness on exchange anisotropy is discussed in detail.Both negative(or positive)H_E and H_C always decrease with increasing of FM thickness t_FM,which shows good agreement with experimental observation.It demonstrates interfacial nature of the exchange anisotropy.However,AFM thickness t_AFM dependence of exchange anisotropy is relatively complex.In the case of positive H_E,with increasing of t_FM,H_E increases and H_c decreases.But。in the valse of negative H_E,H_E decreases and H_C increases with increasing t_AFM.

Phases of antiferromagnetic magnetization and exchange bias and coercivity in ferromagnetic/antiferromagnetic/ferromagnetic(FM/AF/FM) trilayers with interface quadratic and biquadratic exchange coupling are studied comprehensively.Three possible cases are found,namely reversible recovering case,irreversible continuously-reversing case and irreversible discontinuously-reversing case. Realization of the cases strongly depends on pinned-M_FM interface quadratic exchange coupling J₁,free-M_FM interface quadratic exchange coupling J₂ and biquadratic coupling J'₂.In the reversible recovering,the exchange coupling results in an exchange bias,and there is no exchange bias in other cases.It provides possible explanation for both hysteresis energy loss and perpendicular coupling at the interface.