Simulation of Advanced Exchange Coupled Composite Media｜國立清華大學博碩士論文庫

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研究生：	吳宗霖 Tzung-Lin Wu
論文名稱：	Simulation of Advanced Exchange Coupled Composite Media 新穎交互耦合複合式記錄媒體之微磁學模擬研究
指導教授：	賴志煌 Chih-Huang Lai 楊志信 Jyh-Shinn Yang
口試委員:
學位類別：	碩士 Master
系所名稱：	工學院 - 材料科學工程學系 Materials Science and Engineering
論文出版年：	2008
畢業學年度：	96
語文別：	英文
論文頁數：	90
中文關鍵詞：	磁紀錄、微磁學、模擬、數值方法
相關次數：	點閱：4 下載：0
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Exchange coupled composite (ECC) media is one of the potential
candidates in the advanced media design. The basic concept is a reduced
switching field with remaining high thermal stability provided by two
coupled soft and hard magnetic layers. The film structure which is
extended to CoCrPt-SiO /Pt assisting layer of multi-layer design has
2
been realized by experiment [1]. These assisting layers provide a higher
thermal stability and a reduced switching field.

Many complex mechanisms, like the exchange coupling force
between soft layers inside single grain, and the film thickness dependence
on the domain wall assisted reversal behavior, are key issues for further
advanced design on this novel media. But these concepts are not easy to
be verified by experiment.

This article focus on the design of film structure in the point of
micromagnetic simulation, especially about inter-layer coupling strength
and the number of assisting layers. This work begins at single grain
model, and then it is extend to a 7-grain cluster model. In the case of
single model, we find the inter-layer coupling J is critical in the magnetic
property. When it is increasing, we can observe the lower energy barrier
occurs in the reversal process. But if a much larger J is proposed, the
switching field finally increases. This means an optimum coupling
strength exists. The second issue in single grain model is adjusting the

soft layer number. A clear trend illustrated from the modeling result
shows that, the switching field can keep decreasing until the soft layer
number reaches 9. This configuration gives the evident that this critical
thickness is equal to the intrinsic domain wall width. The simulation
works involved here are based on the OOMMF code, developed by M. J.
Donahue and D. G. Porter, NIST.

When the lateral coupling force between grains is introduced, the
grain cluster model performs a result more approaching the real
experiment data. It can ensure the reliability of this work and provide a
powerful guideline for further film structure design.

中文摘要

交互偶合復合式記錄媒體是現今最具潛力的新穎記錄媒體之一。
基本的概念是偶合兩層磁性質差異很大的軟磁和硬磁層，能在保持熱
穩定度的情況下大幅降低翻轉場。多層輔助寫入功能的軟層已經在實
驗上被研究。其中有許多複雜的機制，如軟層間交互偶合力、軟層層
數對磁壁輔助翻轉機制的影響等議題。這些主題在新式的交互偶合復
合式記錄媒體的設計上都相當關鍵，但在實驗上卻不容易被有系統的
討論。

這篇文章使用 OOMMF 微辭學模擬軟體對多層膜(軟層輔助寫入層)
式交互偶合復合式記錄媒體進行微觀磁性分析，分別建立了單顆、雙
顆，和七顆晶粒團簇三種模擬的模型。在單顆的模型內討論軟層間交
互偶合力，和軟層層數對磁壁輔助翻轉機制的影響等議題進行探討。
發現交互偶合力有一最佳值能最優化翻轉場降低。並且當軟磁性輔助
寫入層層數持續增加到晶粒內部磁壁長度時，可以達到最大的反轉場
降低效果。七顆晶粒團簇模型提供中央晶粒更接近真實環境，我們亦
可以由其中觀察到更接近真實實驗數據的結果。顯示了這套模型的可
靠度和對於新式膜層的設計，可以提供一個具參考價值的準則。

Contents
Abstract
Contents
Chapter 1 Introduction………………………………………………………………………….1
Chapter 2 Background ............................................................................. 4
2.1 Finite different method ................................................................... 4
2.1.1 Forward, backward and central
differences…………..……………………………………………………………..…………..4
2.1.2  Finite difference calculation ………………………………………… ….5
2.1.3  Derivatives with high order……………  …………………5
2.1.4  Finite method……………………………………………………………… …6
2.1.5  Finite different operator…………………………………………………………6
  2.2 The finite element micromagnetic model and dynamic
equation………………………………………………………………………………………..7
2.2.1 Free energy concern in micromagnetics….………………………… 10
2.2.1.1Continuum hyposis………………………….………………………………11
2.2.1.2 Anisotropy energy…………………………………………………………..11
2.2.1.3 Exchange energy and interaction……………………………… .…12
2.2.1.4 Magnetostatic energy…………………………………………………....13
2.2.1.5 External induced Zeeman energy………………………………….. 4
2.2.1.6 Free energy expression…………………………………………………..14
        2.2.2 The dynamic equation……………………………………………………..14
          2.2.2.1 Gyromagnetic prwssion…………………………………………………. 5
          2.2.2.2 The Landau – Lifshitz – Gilbert equation………………… 5
2.3 Micromagnetic simulation development and current state… 6
2.4 Exchange Coupled Composite(ECC) media …………………… ……...22


Chapter 3 Experiment design and simulation  ………………………..37
    3.1 Experiment flow chart………………………………………………………………37
3.2 Software and Numerical Micromagnetic mode 38

Chapter 4 Results and discussions……………………………………………………….40
    4.0.1 Introduction…………………………………………………………………………..40
  4.0.1 Introduction………………………………………………………………………40
   4.0.2 Result and discussion…………………………………………………………40
4.1 Demagnetization field fact in single grain system 42
    4.1.1 Introduction……………………………………………… …………………42
4.1.2 Simulation model detail…………… ………………..………..43
4.1.3 Results and discussions……………………… ...................44
4.1.4 Conclusions………………………………………… ……………………….47
  4.2 Modified inter-layer exchange coupling  J  in single grain
system………………………………………………………………………………………48
   4.2.1 Introduction……… ……………………..………………………………….48
4.2.2 Simulation model detail………………… ………………..…..49
4.2.3 Results and discussions……………………… ...................50
4.2.4 Conclusions………………………………………… ……………………….58
4.3 Soft layer number dependence………………………………………………..59
4.3.1 Introduction………………………………………………………………… 59
4.3.2 Results and discussions………………………… ...................59
4.3.3 Conclusions…………………………………………… ……………………….64
   4.4 Double grains model………………………………………………………………..67
4.4.1Introduction………… ……………………..…………………………………..67

4.4.2 Simulation model detail………………… ………………..…..67
4.4.3 Results and discussions……………………… ...................68
4.4.4 Conclusions………………………………………… ……………………….71
    4.5 Seven-grains cluster model……………………………………………………….71
          4.5.1 Introduction………………………………………………………………………71
          4.5.2 Simulation model detail…………………………………………………….72
       4.5.3 Result and discussion……………………………………………………….74.
          4.5.4 Conclusions……………………………………………………………………….77

Chapter 5 Summary .. ...78

















List of figures

Figure 2.2.1  ..9
Figure 2.2.2  ..10
Figure 2.3.1 Finite element method of models .. ..11
Figure 2.3.2 D .18
Figure 2.3.3 Meshing process ..20
Figure 2.3.4 Nmag micromagnetic simulation 21
Figure 2.3.5 The multi-scale modeling mes ...22
Figure 2.4.1 The micromagnetic modeling of hard/soft
bilayer  ...24
Figure 2.4.2 Magnetization reversal configuration by OOMMF code....26
Figure 2.4.5  ...  28
Figure 2.4.6 Domain wall spin configuration under an  .  29
Figure 2.4.7  ..30
Figure 2.4.8 Stereographic projection of the unit- .31
Figure 2.4.9 The dependence of coupling force and switching field in
F ...32
Figure 2.4.10.  ..34
Figure 2.4.11. MH loop and dynamic moment tilting distribution in  .35
2
Figure 2.4.12. 1 T bit /in   ..36
Figure 3.0  ...39
Figure 4.0.1  ..41

Figure 4.1.1 The derived equation of D  and corresponding coordinate
Z .43
Figure 4.1.2 The film structure in section 4.1 ..44
Figure 4.1.3 Hysteresis loops demonstrate the effect of demagnetization  ...45
Figure 4.1.4 Demagnetization field inside the  47
Figure 4.2.1 Simulation model detail in section 4.2 for film  50
Figure 4.2.2 Hysteresis loops for different coupling strength J ...51
Figure 4.2.3 The vertical spin configuration inside the grain during  54
2
Figure 4.2.4 Inter-spacer exchange energy J is equal to 0.6 erg/cm and
2
1.2 erg/cm .55
Figure 4.2.5  ..57
Figure 4.2.6 Reversal process for each soft layer 58
Figure 4.3.1  59
Figure 4.3.2 The curves of the interface exchange energy across each Pt  ..60
Figure 4.3.3  ...62
Figure 4.3.4 Time resolved demagnetization curve illustrates the upper  63
Figure 4.3.5  ..66
Figure 4.4.1 Double grains model ...68
Figure 4.4.2 The corresponding demagnetization curves of single and  69
Figure 4.4.3 The demagnetization curve of different degree of
the  70

Figure 4.5.1 Construction for grain cluster model ...73
Figure 4.5.2 The illustration of 7- .74
Figure 4.5.3  75
Figure 4.5.4 The measured MH loop for different soft layer number .76

                                

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