磁気ヘッドの再生素子に用いられる反強磁性膜について,再生ギャップ長を低減させるための薄膜化を目的とし,反強磁性(AFM)と強磁性(FM)積層膜における交換バイアスについてハイゼンベルグ模型を用いた検討を行った.交換バイアスのAFM膜厚依存性をLandau-Lifshitz-Gilbert方程式を解いて求めた.AFM層の合金構造を不規則γ相,L1_2型規則相およびL1_0型規則相とするとそれぞれのスピン構造はトリプルQ(3Q)構造,T1構造およびAF-I構造となった.交換バイアスは積層膜界面における磁壁に影響され,磁壁幅で規定されるAFM層の臨界膜厚はスピン構造によって変化する結果となった.それぞれのスピン構造に対する臨界膜厚d_c~(3Q),d_c~(T1)およびd_c~(AF-I)の間には3~(1/2)d_c~(3Q)=2~(1/2)d_c~(T1)=d_c~(AF-I)の関係があることが明らかになった.%For the material design of thin exchange bias layer to reduce the read gap length, the exchange bias between the ferromagnetic(FM) and antiferromagnetic(AFM) bilayer was investigated within the framework of the classical Heisenberg model. The dependence of the exchange bias on the AFM layer thickness was also calculated by using the Landau-Lifshitz-Gilbert equation. The triple-Q(3Q), T1 and AF-I spin structures are obtained in the disordered 7-phase, ordered L1_2- and L1_0-type lattices, respectively. The exchange bias is caused by the formation of the interfacial domain wall in the AFM layer, and the critical thickness d_c of AFM layer is dominated by the varied spin structures. Consequently, the relation of the critical thickness can be represented as 3~(1/2)d_c~(3Q) = 2~(1/2)d_c~(T1) = d_c~(AF-I).
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