交换偏置系统中的反铁磁磁化与自旋波

采用自由能变分法研究了铁磁/反铁磁双层膜系统在反铁磁层存在净磁化下的自旋波谱.本模型中铁磁薄层具有单轴磁晶各向异性和立方磁晶各向异性，反铁磁层仅具有单轴磁晶各向异性，但厚度有限，推导出了系统铁磁共振频率的表达式.结果表明：系统的自旋波谱分光学模和声学模两种，其中光学模仅在反铁磁层存在净磁化时得到激发.自旋波谱可按外磁场强度的变化情况分为强弱两支；区分强磁场和弱磁场的临界场依赖于铁磁/反铁磁间的交换作用，反铁磁层的磁化强度以及反铁磁层的厚度等.交换偏置场对光学模的影响明显于声学模，而反铁磁的净磁化和其厚度对系统的影响紧密联系，难以区分.但当反铁磁层净磁化很小可忽略时，系统只存在声学模激发. 关键词： 铁磁/反铁磁双层膜 反铁磁层净磁化 光学模 声学模

The magnetization of antiferrmagnetic layer and the spin wave in the system of the exchange bias

Using a method of free energy minimization，the spin wave of ferromagnetic （FM）/antiferromagnetic （AFM） bilayers was investigated，in which the net magnetization of AFM layer has been considered. In this model，the thin FM layer is taken to be a single crystal with cubic and uniaxial magnetocrystalline anisotropies，but AFM layer has only single uniaxial magnetocrystalline anisotropy and its thickness is finite. Numerical calculation shows that there are two modes of spin waves：namely the acoustic mode and the optical mode. Moreover, only when there is net magnetization of AFM layer can the optical mode be observed. There are two branches of FMR curves，i.e. the branches of weak and strong external field，which are distinguished by the critical field，while the critical field depends on the exchange bias field，the magnetization and thickness of AFM layer. The effect of the exchange bias field on the optical mode is more obvious than that on the acoustic mode，while the effects groduced by net magnetization and thickness of AFM layer cant be distinguished. However，when the net magnetization of AFM layer is neglected，only an acoustic mode is observed.