Reversal Mechanism of Exchange-Biased CoFeB/IrMn Bilayers Observed by Lorentz Electron Microscopy
Reversal Mechanism of Exchange-Biased CoFeB/IrMn Bilayers Observed by Lorentz Electron Microscopy
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DOI：
10.1109/tmag.2009.2024900
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发表时间：
2009-09
影响因子：
2.1
通讯作者：
András Kovács;A. Kohn;J. Dean;T. Schrefl;A. Zeltser;Matthew J. Carey
中科院分区：
文献类型：
--
作者：
András Kovács;A. Kohn;J. Dean;T. Schrefl;A. Zeltser;Matthew J. Carey
利用洛仑兹透射电子显微镜研究了具有不同反铁磁层厚度的交换偏置薄膜的磁化反转机制。多晶IrMn和非晶CoFeB双层膜表现出单向各向异性，这是由场退火引起的。洛伦兹分析表明，磁矩旋转远离单向轴反转之前，当施加的磁场是共线的单向各向异性方向。根据振动样品磁强计和电子显微镜观察，在这些层中没有发现反转过程的不对称性。小的（直径<10 μ m）360度畴壁环用作反转的成核位点，并且在反转期间消失。当磁场垂直于单向轴施加时，观察到磁矩的连续旋转。轻微的混合在界面和结构缺陷，如界面粗糙度，晶界，和堆垛层错被确定为磁挫折和未补偿的自旋在IrMn层，有助于交换偏置的可能来源。
The magnetization reversal mechanism of exchange-biased thin layers with different antiferromagnetic (AFM) layer thicknesses has been investigated using Lorentz transmission electron microscopy. The polycrystalline IrMn and amorphous CoFeB bilayers exhibit unidirectional anisotropy, which was induced by field annealing. Lorentz analyses revealed that the magnetic moments rotate away from the unidirectional axis before reversal, when the magnetic field was applied collinear to the unidirectional anisotropy direction. No asymmetry of the reversal process was found in these layers according to the vibrating sample magnetometry and electron microscopy observation. Small ( <10 mum in diameter) 360deg domain-wall loops act as nucleation sites for reversal and disappear during the reversal. A continuous rotation of magnetic moments was observed when the magnetic field was applied perpendicular to the unidirectional axis. Minor intermixing at the interface and structural defects such as interface roughness, grain boundaries, and stacking faults were identified as possible sources of magnetic frustration and uncompensated spins in the IrMn layer that contribute to exchange bias.