Electronic structure and magnetic properties of magnetically dead layers in epitaxial CoF e 2 O 4 /A l 2 O 3 /Si (111 ) films studied by x-ray magnetic circular dichroism
Electronic structure and magnetic properties of magnetically dead layers in epitaxial CoF e 2 O 4 /A l 2 O 3 /Si (111 ) films studied by x-ray magnetic circular dichroism
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DOI：
10.1103/physrevb.96.104410
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发表时间：
2017-04
影响因子：
3.7
通讯作者：
Y. Wakabayashi;Y. Nonaka;Y. Takeda;S. Sakamoto;K. Ikeda;Z. Chi;G. Shibata;A. Tanaka;Y. Saitoh;H. Yamagami;Masaaki Tanaka;A. Fujimori;R. Nakane
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文献类型：
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作者：
Y. Wakabayashi;Y. Nonaka;Y. Takeda;S. Sakamoto;K. Ikeda;Z. Chi;G. Shibata;A. Tanaka;Y. Saitoh;H. Yamagami;Masaaki Tanaka;A. Fujimori;R. Nakane
由于CoFe_2 O_4的自旋过滤效应，CoFe_2 O_4/Al_2 O_3双层外延膜有望成为Si中高效的自旋注入器。为了充分利用该系统的潜力，了解磁死层的微观起源在CoFe 2 O 4/Al 2 O3界面是必要的。本文研究了不同厚度的CoFe_2O_4（111）薄膜的晶体结构、电子结构和磁性（厚度d = 1.4，2.3，4，利用软X射线吸收谱（XAS）和X射线磁圆二色性（XMCD）结合团簇分析技术，研究了CoFe_2 O_4（111）/Al_2 O_3（111）/Si（111）外延结构中的（10 nm和11 nm）纳米晶间的相互作用。模型计算通过XMCD测量的CoFe 2 O 4的磁化强度随着厚度d的减小而逐渐减小，并且最终在d = 1.4nm处清楚地检测到磁死层。磁死层具有磁相互作用的挫折，这是从在300和6 K的磁化强度之间的比较中揭示的。从使用组态相互作用簇模型计算的分析，d的减少导致反尖晶石结构比的减少，并且在八面体位置处的Fe的平均价态也减少。这些结果强烈表明，磁死层在CoFe 2 O 4/Al 2 O3界面起源于各种复杂的网络的超交换相互作用，通过在晶体结构和电子结构的变化。此外，从d = 1.4和2.3 nm之间的磁性能的比较，发现在d = 1.4 nm处的磁死层的亚铁磁顺序通过在其上附加生长0.9 nm厚的CoFe 2 O 4层而恢复。
Epitaxial CoFe2O4/Al2O3 bilayers are expected to be highly efficient spin injectors into Si owing to the spin filter effect of CoFe2O4. To exploit the full potential of this system, understanding the microscopic origin of magnetically dead layers at the CoFe2O4/Al2O3 interface is necessary. In this paper, we study the crystallographic and electronic structures and the magnetic properties of CoFe2O4(111) layers with various thicknesses (thickness d = 1.4, 2.3, 4, and 11 nm) in the epitaxial CoFe2O4(111)/Al2O3(111)/Si(111) structures using soft X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) combined with cluster-model calculation. The magnetization of CoFe2O4 measured by XMCD gradually decreases with decreasing thickness d and finally a magnetically dead layer is clearly detected at d = 1.4 nm. The magnetically dead layer has frustration of magnetic interactions which is revealed from comparison between the magnetizations at 300 and 6 K. From analysis using configuration-interaction cluster-model calculation, the decrease of d leads to a decrease in the inverse-to-normal spinel structure ratio and also a decrease in the average valence of Fe at the octahedral sites. These results strongly indicate that the magnetically dead layer at the CoFe2O4/Al2O3 interface originates from various complex networks of superexchange interactions through the change in the crystallographic and electronic structures. Furthermore, from comparison of the magnetic properties between d = 1.4 and 2.3 nm, it is found that ferrimagnetic order of the magnetically dead layer at d = 1.4 nm is restored by the additional growth of the 0.9-nm-thick CoFe2O4 layer on it.