Fe_3O_4单晶薄膜磁性电场调控的微磁学仿真研究

磁性薄膜磁学特性电场调控的相关研究对开发新型低功耗磁信息器件具有突出意义.本文基于电场调控磁性的基本理论,以OOMMF(Object Oriented Micro-Magnetic Frame)微磁学仿真软件为工具,研究了电场对生长于PZN-PT单晶衬底上Fe_3O_4单晶薄膜磁学特性的调控.研究结果显示:无外加电场时,薄膜表现出典型的软磁特性;沿衬底001]方向施加的外加电场可以使得薄膜矫顽力、矩形比等磁学特性发生显著改变:当外加磁场沿100](010])时,施加正值(负值)电场强度可以显著增大薄膜的矫顽力与矩形比,当电场强度不小于0.6 MV/m时薄膜矩形比达到1.这是因为外加电场导致薄膜产生单轴应力各向异性,使得薄膜的等效磁各向异性发生了从无外电场下的面内四重磁晶各向异性向高电场下的近似单轴磁各向异性的过渡.外加1 MV/m与-1 MV/m的电场时等效易磁化轴分别沿100]与010]方向.另外,外加1 MV/m(-1 MV/m)的电场强度可以使得铁磁共振的频率增大(减小)接近1 GHz.

Electric-field control of magnetic properties of Fe3O4 single-crystal film investigated by micro-magnetic simulation

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 the100]and010]crystallographic directions of Fe₃O₄ and an electric field applied along the001]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 the100]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 the010]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 the100]and010]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.