摘要
在Heisenberg模型的基础上,采用界面重参数化方法(Interface-rescaling approach),严格求解了简立方结构双层铁磁薄膜中自旋波的本征问题,且主要讨论了外磁场对体系能带结构和自旋波的影响。通过对所选体系进行数值计算和作图发现,外磁场对能带有以下三个方面的影响：(1)随着磁场的增强,子能带A、B都向上移动,且B带移动的速度远大于A带,表明22支模的能量随着磁场的增强都在增加,且B带中模的能量增加的快；(2)体模随横向自旋波γ值的变化基本呈周期性振荡变化,且随着磁场的增加,体模部分也在不断上移,说明能量也在不断增加,当磁场取某一临界值时,能带A、B处于分离状态,体模完全消失；(3)随着磁场的改变,界面模和禁闭模之间发生转换,且随着磁场的增加,界面模逐渐远离A带。另外磁场对自旋波的影响也存在以下三个方面：(1)磁场对自旋波波形有影响,它表现在通过改变磁场的值可以改变波的类型；(2)磁场对自旋波的调制现象有影响,当磁场达到某一临界值时,调制现象就消失了；(3)磁场对自旋波的振荡现象也有影响,我们发现改变磁场的值可以改变波形的振荡现象。
On the basis of the Heisenberg exchange model, the spin-wave eigen-problem in the ferromagnetic bilayers with simple cubic structure is solved exactly at the low temperature. With this theory, we focus on the effect of the magnetic field on the system band structure and spin waves in the paper. The results show that the magnetic field effected energy bands in three aspects as follows:(1) With the increasing of the magnetic field, band A and B are both moving up, and B moves faster than A. This phenomenon means that the energy of all the modes increases, and the energy of band B increases faster. (2) Bulk modes change with transverse spin waves periodically, and with the increase of the magnetic field, bulk modes move up too. When the magnetic field takes a certain critical value, band A and B are separation, moreover the bulk modes disappear. (3) As the magnetic field changes, the conversion takes between the interface modes and bulk modes, and with the magnetic field, the interface modes move away from band A. The effect of magnetic field on spin waves exists in the following three aspects:(1) The magnetic field influence on the waveform, which is exhibited in the type of the spin waves can be changed when the magnetic being changed. (2) The magnetic field have effect on the phenomenon of the spin wave modulation. When the magnetic field reaches a certain critical value, the modulation phenomenon disappears. (3) The magnetic field also have an impact on the spin-wave oscillations. We find that the oscillation of the waveform can be changed by the magnetic field excitation.
引文
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