外应力下交换偏置双层膜角度关系曲线的中心偏移现象  

Center Shift Phenomenon of the Characteristic Curves for Exchange-Bias Bilayers under External Stress

作　　者：郭子政[1] 胡旭波[1] 罗志环[1] 

机构地区：[1]华南农业大学理学院应用物理系,广东广州510642

出　　处：《高压物理学报》2013年第5期738-744,共7页Chinese Journal of High Pressure Physics

基　　金：广东省高等学校引进人才专项资金;华南农业大学校长科学基金

摘　　要：研究了外应力与易轴夹角为任意角度Ψ时铁磁/反铁磁双层膜中交换偏置对外磁场取向角θ0的的依赖关系,特别是矫顽力和偏置场曲线的中心偏移现象。由于斯通纳-沃尔法斯模型和能量极小原理只能给出θ0部分取值下的矫顽力解析表达式,将不满足能量极小原理的θ0取值部分的矫顽力用转换场近似,得到矫顽力的分段函数形式。数值计算显示,矫顽力和偏置场角度关系曲线是否发生中心偏移与Ψ取值有关:Ψ=π/4时,应力造成等效各向异性场强度的改变,并造成矫顽力和偏置场曲线中心的偏移;Ψ=π/2时,应力只改变等效各向异性场强度,而矫顽力和偏置场曲线不发生中心偏移。因此发生曲线中心偏移的条件是有效各向异性场对易轴的夹角θ*不为零。另外,只有θ*≠0时,才能发生交换偏置场的阶跃现象,说明该阶跃现象是转换场在θ*附近奇点造成的。Focusing on the center shift phenomenon of the coercivity curves and the exchange bias field curves, the dependences of the exchange bias on θ0, the angle of external field orientation, in ferromagnetic/antiferromagnetic bilayers are studied in the cases that Ψ, the angle between the stress field and the easy axis, is taken as π/4 or π/2. It is shown that the analytical expression of the coercivity cannot be derived by using the Stoner-Wohlfarth model and the principle of energy minimum for the whole range of the angle θ0. We approximate the coercivity with the switching field for the θ0 interval at which the principle of energy minimum is not satisfied, and in this way, we got the coercivity expression in the form of piecewise function. Numerical calculations indicate that whether the center shift phenomenon of the coercivity curves and the exchange bias field curves occurs depends on the value of Ψ. While Ψ=π/4, stress results in not only the change of the strength of the effective anisotropic field but the center shift of coercivity curves and the exchange bias field curves; while Ψ=π/2, only the strength of the effective anisotropic field is influenced and no such center shift occurs. The condition in which the center shift of the coercivity curves and the exchange-bias field curves occurs is that θ＊, the angle of the effective anisotropy field to the easy axis, is not equal to zero. In addition, the results also show that the jump phenomenon can only be observed while θ＊≠0, implying that the jump phenomenon is caused by the singularity of the switching field near θ＊.

关 键 词：铁磁 反铁磁双层膜 交换偏置 应力 矫顽力 

分 类 号：O484.43[理学—固体物理]