| 层间耦合多层膜的高频动力学行为 |
| Alternative Title | High frequency dynamics of multilayer with interface exchange coupling
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| 汪文峰 |
| Thesis Advisor | 薛德胜
; 柴国志
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| 2019-04-08
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| Degree Grantor | 兰州大学
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| Place of Conferral | 兰州
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| Degree Name | 博士
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| Degree Discipline | 凝聚态物理
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| Keyword | 层间交换耦合
光学支铁磁共振
多层膜
高频磁性
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| Abstract | 交换作用广泛存在于磁性材料内部和不同材料的界面处。由层间耦合引起的诸如转动各向异性、光学支铁磁共振、巨磁电阻效应和交换偏置效应等为薄膜材料的性能研究提供了新的方向和思路。发现层间耦合的新规律，调控多层膜的高频磁性已然成为目前的研究热点。本论文以层间交换耦合铁磁多层膜为载体，重点开展了转动各向异性、光学支铁磁共振和层间交换耦合低温特性的研究，取得的创新性结果如下： 1. 在Fe20Ni80/FeMn双层薄膜中实现了无偏置转动各向异性。调控层间交换耦合实现了无偏置的转动各向异性，得到了面内360°不为零的磁导率；实验上成功地区分了单向和转动各向异性，验证了Stiles等人关于交换偏置和转动各向异性分别来源于反铁磁晶粒的可逆和不可逆转动的理论。 2. 发现了Fe20Ni80/Co双层膜界面处的交换场与膜厚的平方成反比。对比声学支共振频率的变化规律，发现光学支的共振频率随Fe20Ni80的厚度增加而减小，其主要原因是层间交换耦合场的减小。拟合声学支和光学支的共振频率-磁场曲线，发现耦合场Hex和膜厚t满足Hex~t-2)，交换耦合常数A=0.57×10-6 erg/cm。在Co层中掺入Zr元素改变层间交换耦合可进一步调控光学支共振频率。 3. 发现了Fe20Ni80/Co双层膜的光学支磁导率随外磁场增加而增加。构建了层间耦合双层膜的磁化强度动力学模型，得到了双层膜的色散关系和磁导率表达式。结合实验结果，证明了两层磁矩的反相位进动导致了光学支磁导率的增加。理论计算还发现随着外场增加，光学支磁导率先增加后减小，极值点对应的磁场不仅与膜厚有关，而且与外加磁场的方向有关。 4. 发现Fe20Ni80/Co双层膜的交换耦合常数Jinter与温度Ty的关系中y<1。测量了不同温度下Fe20Ni80/Co双层膜的变频扫场铁磁共振，证明了Jinter (T)和T的关系满足： Jinter (T)/Jinter (0)≈1-xTy。其中，y=0.59远小于文献中给出的1.5，这一不同可能来自于铁磁层的饱和磁化强度差异。 |
| Other Abstract | Exchange interaction is widely found within magnetic materials and interface between different materials. Rotatable anisotropy, optical ferromagnetic resonance, giant magnetism resistance and exchange bias effect caused by interface exchange coupling provide a new way for the study of thin film materials. It has become a research hotspot to discover the new properties of interface exchange coupling and regulate high frequency magnetic properties of multilayers. This thesis focuses on the research of rotatable anisotropy, optical ferromagnetic resonance, and magnetic properties at low temperature based on the interface exchange coupled ferromagnetic multilayers. The main results are as follows: 1. Unbiased rotatable anisotropy has achieved in Fe20Ni80/FeMn bilayer. In-plane omnidirectional permeability of the bilayer was detected by regulating interface exchange coupling. In experiment, we successfully stripping the rotatable anisotropy from ferro-antiferromagnetic exchange coupled bilayer，and verified the theory of Stiles et. al about the exchange bias systems that the exchange bias effect and the rotatable anisotropy originate from reversible and irreversible rotation of antiferromagnetic grains, respectively. 2. The interface exchange coupling field of Fe20Ni80/Co bilayer was found to be inversely proportional to square of the layer thickness. Compared with the variation of acoustic mode, the optical resonance frequency decreases with the increase of Fe20Ni80 layer thickness, which is mainly caused by the decrease of interface exchange coupling. By fitting f-H curve of acoustic and optical resonance, it was found that the variation of coupling field with layer thickness satisfy Hex~A/t2 , where exchange constant A=0.57×10-6 erg/cm. The interface exchange coupling can be regulated by doping Zirconium in Co layer, and thus the optical resonance frequency can be changed. 3. We found that optical permeability of Fe20Ni80/Co bilayer increases with the increase of external magnetic field. We proposed a theoretical model for dynamical response of the magnetization of interface exchange coupled magnetic bilayer. The expressions for dispersive relation and permeability of the bilayer were derived. Combining with experimental results, we proved that the increase of optical permeability is originated from out-of-phase precession of the two layers' magnetic moments. The calculations based on the theoretical model show that the optical permeability increases firstly with the increase of external field and then decreases as the field continues to increase. The critical field where the permeability reaches extreme value is closely related to layer thickness and the directions of external field. 4. In Fe20Ni80/Co bilayer, the relation between the exchange intensity Jinter and temperature Ty gives y<1. The variable frequency sweeping field ferromagnetic resonance at different temperature was obtained via PPMS measurements, proving that Jinter (T) and T satisfy Jinter (T)/Jinter (0)≈1-xTy. The fitting parameter y=0.59, is much less than the value of 1.5 given by references. Such a difference might result from discrepancy between saturation magnetizations of the ferromagnetic layer. |
| Pages | 100
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| URL | 查看原文
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| Language | 中文
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| Document Type | 学位论文
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| Identifier | https://ir.lzu.edu.cn/handle/262010/343118
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| Collection | 物理科学与技术学院
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| Affiliation | 物理科学与技术学院
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| First Author Affilication | School of Physical Sicence and Technology
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Recommended Citation
GB/T 7714 |
汪文峰. 层间耦合多层膜的高频动力学行为[D]. 兰州. 兰州大学,2019.
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