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Improved magnetic anisotropy of Co-based multilayer film with nitrogen dopant

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Abstract

Modulating the magnetic anisotropy of ferromagnetic thin films is crucial for constructing high-density and energy efficient magnetic memory devices. Ta/W(N)/Co/Pt multilayers were deposited on silicon substrates by magnetron sputtering at room temperature. The influences of N dopant on the magnetic anisotropy of the multilayers were investigated by preparing the sample with N incorporation. The results indicate that when sputtering W target with only argon gas (Ar), Ta/W/Co/Pt sample shows in-plane magnetic anisotropy (IMA). When sputtering W target at a different amount of N2 and Ar atmosphere, it can induce perpendicular magnetic anisotropy (PMA) for proper N-doped Ta/W(N)/Co/Pt sample. When the gas flow ratio of Ar:N2 is 16:6, the effective magnetic anisotropy constant reach its maximum value of 1.68 × 105 J·m−3, which enhanced by about 400% than our past works (annealing treatment is necessary to induce PMA in Pt/Co/MgO system). X-ray diffraction (XRD) and X-ray reflection (XRR) results demonstrate that N dopants can effectively promote the formation of β-W phase and reduce the roughness of W(N)/Co interface, which are beneficial for PMA. X-ray electron spectroscopy (XPS) analysis reveals that N doping redistributes Co charges, nitrogen ions participate in electron allocation of Co and attract some electrons of Co to form orbital hybridization between Co 3d and N 2p. This may be another important reason for the PMA formation.

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摘要

调控铁磁薄膜的磁各向异性对构建高密度、低能耗磁存储器件的至关重要。本工作利用磁控溅射系统在室温下制备了Ta/W(N)/Co/Pt多层膜, 研究了氮的掺杂对薄膜磁各向异性的影响。实验结果表明 : 在W层沉积时未通入氮气制备的Ta/W/Co/Pt样品在制备态下呈现面内磁各向异性 (IMA) ; 而在W层沉积时适当的通入氮气, 可以有效地促进样品由面内磁各向异性向垂直磁各向异性 (PMA) 转化。当氩气和氮气比 (简称氩氮比) Q=16:6时, 无需经过退火处理, 在制备态下样品的磁各向异性常数Keff高达1.68×106 erg/cm3。此性能比我们之前报道的Pt/Co/MgO体系提升了约4倍 (需退火处理才呈现PMA, 约为0.4×106 erg/cm3)。通过X射线衍射 (XRD) 和X射线反射 (XRR) 测试分析发现在制备W层时适当的氮掺杂有利于β-W相的形成, 并且降低了W(N)/Co的界面粗糙度, 这有利于样品垂直磁各向异性的产生。另外, 根据X射线衍射 (XRD) 和X射线反射 (XRR) 结果可知N的掺杂有效促进β-W的形成并降低W/Co(N)的界面粗糙度, 从而有利于PMA的产生。X射线光电子能谱 (XPS) 测试结果推测, 氮的掺杂使得W/Co界面上Co原子的电荷重新分布, 氮离子参与了Co的电子分配, 吸引Co的部分电子形成Co 3d和N 2p轨道杂化, 从而调节了W(N)/Co界面处电子的轨道杂化状, 这可能是样品由面内磁各向异性向垂直磁各向异性转变的另一个重要原因。

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Acknowledgements

This work was financially supported by the National Key Research and Development Program of China (No. 2019YFB2005800), the National Science Foundation of China (Nos. 51871017, 51871018 and 52071025), Beijing Natural Science Foundation (No. 2192031), the Fundamental Research Funds for the Central Universities (No. FRF-TP-19-011B1) and the Foundation of Beijing Key Laboratory of Metallic Materials and Processing for Modern Transportation.

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Authors and Affiliations

  1. School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing, 100083, China

    Ling-Ran Yu, Xiu-Lan Xu, Yun-Long Jia, Xu-Jie Ma, Yong-Hui Zan, Chun Feng & Jiao Teng

  2. School of Civil and Resources Engineering, University of Science and Technology Beijing, Beijing, 100083, China

    Xuan Geng

  3. School of Mathematics and Physics, University of Science and Technology Beijing, Beijing, 100083, China

    Yi-Fei Ma

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  1. Ling-Ran Yu
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Correspondence to Xiu-Lan Xu or Jiao Teng.

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Yu, LR., Xu, XL., Jia, YL. et al. Improved magnetic anisotropy of Co-based multilayer film with nitrogen dopant. Rare Met. 40, 2855–2861 (2021). https://doi.org/10.1007/s12598-021-01732-1

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