Control of magnetic properties by an applied electric field has significant potential applications in the field of novel magnetic information devices,with some advantages such as low dissipation and small sizes.Till now,many scientific and technical problems in this field have been widely investigated theoretically and experimentally.However,a lacuna still exists in the papers concerning the investigations performed by micromagnetic simulation which is a powerful tool for revealing magnetic behaviors in a complicated magnetic system.Based on the basic principle for electric-field manipulation of magnetic properties,we study the electric-field control of magnetic properties of a square-shaped singlecrystal Fe3O4 thin film formed on a single-crystal PZN-PT piezoelectric substrate by the micromagnetic simulation method via object oriented micro-magnetic frame (OOMMF),a software for micromagnetic simulation.The magnetic hysteresis loops are collected for the Fe3O4/PZN-PT composite system under magnetic fields applied in the[100]and[010]crystallographic directions of Fe3O4 and an electric field applied along the[001]axis of the PZN-PT substrate. The applied electric field acts as an stress anisotropy energy.The result of our simulation is similar to the reported result of an experimental investigation for the same system and is consistent with that of our theoretical analysis based on a thermodynamic route.The results reveal that the film exhibits typical soft-magnetic behavior without applying an electric field.When an electric field is applied to the PZN-PT substrate,the coercivity and squareness ratio of Fe3O4 is greatly affected.Under an external magnetic field along the[100]axis of Fe3O4,the applying of a positive electric field clearly enhances the coercivity and squareness ratio.On the other hand,when an external magnetic field is applied along the[010]direction of Fe3O4,the coercivity and squareness ratio is increased by applying a negative electric field.In both cases,the coercivity and squareness ratio reaches 1 when the absolute value of E is 0.6 MV/m or larger.This high coercivity and squareness ratio is vital to magnetic information memory.These results are attributed to the competition between an electric-field-induced uni-axial stress anisotropy energy and the intrinsic in-plane four-fold magnetocrystalline anisotropy energy of a Fe3O4 thin film.When the absolute value of E is sufficiently large (1 MV/m), the electric-field-induced stress anisotropic energy significantly overweighs the intrinsic magnetocrystalline anisotropy energy,and the Fe3O4 thin film exhibits an approximate uniaxial magnetic anisotropy energy.Under the electric fields of 1-MV/m and -1-MV/m,the effective easy axis is along the[100]and[010]direction of the Fe3O4 thin film,respectively. Additionally,we also find that applying a 1-MV/m (-1-MV/m) electric-field can cause the frequency for ferromagnetic resonance to increase (reduce) almost 1 GHz,offering the possibility of developing a microwave device with tunable frequency.