Boundary effects in magnetization reversal induced by dipole-dipole interaction in micro-square ferromagnetic films are studied by means of spin dynamics simulation.Fixing strength of dipole-dipole interaction,coercive force is calculated as functions of strength of uniaxial anisotropy and magnetization angle θ (the angle between applied field and easy axis).Typical hysteresis loops and spin configurations are given.It shows that shape of hysteresis loop and magnitude of coercive force are determined by a competition between boundary pinning effect and uniaxial anisotropic field,which leads to different coercivity mechanism under different θ.An effective five-magnetic-domain model is proposed to describe spin configurations of square ferromagnetic thin films.The model shows conveniently geometric and physical properties of square ferromagnetic thin films with uniaxial anisotropy as well as its magnetization reversal process.

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.

The exchange bias and coercivity of FM/AFM bilayers and FM/AFM mixed monolayers with nonmagnetic dilution are studied in a Monte Carlo model.It shows that the exchange bias increases and then decreases with the increasing of dilution concentration while the coercivity decreases and then increases. With the same dilution concentration, both the exchange bias and the coercivity of the regular dilution are stonger than those of random dilution in FM/AFM bilayers.But in the mixed monolayer,the exchange bias of regular dilution is weaker than that of random dilution while the coercivity becomes stronger.Regular dilution results asymmetry in the hysteresis loops distinctly.It shows that the asymmetry of hysteresis loops in FM/AFM systems depends on the interface microstructure.