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Effect of seed layer thickness on the Ta crystalline phase and spin Hall angle
Nanoscale ( IF 5.8 ) Pub Date : 2021-11-26 , DOI: 10.1039/d1nr06007d
K Sriram 1 , Jay Pala 1 , Bibekananda Paikaray 1 , Arabinda Haldar 2 , Chandrasekhar Murapaka 1
Affiliation  

Heavy metal–ferromagnet bilayer structures have attracted great research interest for charge-to-spin interconversion. In this work, we investigated the effect of the permalloy (Py) seed layer on the tantalum (Ta) polycrystalline phase and its spin Hall angle. Interestingly, for the same deposition rates the crystalline phase of Ta deposited on the Py seed layer strongly depends on the thickness of the seed layer. We observed a phase transition from α-Ta to (α + β)-Ta while increasing the Py seed layer thickness. The observed phase transition is attributed to the strain at the interface between the Py and Ta layers. Ferromagnetic resonance-based spin pumping studies reveal that the spin-mixing conductance in the (α + β)-Ta is relatively higher as compared to the α-Ta. Spin Hall angles of α-Ta and (α + β)-Ta are obtained from the inverse spin Hall effect (ISHE) measurements. The spin Hall angle of (α + β)-Ta is estimated to be θSH = −0.15 ± 0.009 which is relatively higher than that of the α-Ta. Our systematic results connecting the phase of Ta with the seed layer and its effect on the efficiency of spin to charge conversion might resolve ambiguities across various literature and open up new functionalities based on the growth process for emerging spintronic devices.

中文翻译:

籽晶层厚度对Ta晶相和自旋霍尔角的影响

重金属-铁磁体双层结构在电荷-自旋相互转换方面引起了极大的研究兴趣。在这项工作中,我们研究了坡莫合金 (Py) 籽晶层对钽 (Ta) 多晶相及其自旋霍尔角的影响。有趣的是,对于相同的沉积速率,沉积在 Py 晶种层上的 Ta 的结晶相强烈依赖于晶种层的厚度。我们观察到从 α-Ta 到 (α + β)-Ta 的相变,同时增加了 Py 种子层的厚度。观察到的相变归因于 Py 和 Ta 层之间界面处的应变。基于铁磁共振的自旋泵浦研究表明,与 α-Ta 相比,(α + β)-Ta 中的自旋混合电导率相对较高。α-Ta 和 (α + β)-Ta 的自旋霍尔角是从逆自旋霍尔效应 (ISHE) 测量中获得的。(α + β)-Ta 的自旋霍尔角估计为θ SH = -0.15 ± 0.009,相对高于 α-Ta。我们将 Ta 相与种子层连接起来的系统结果及其对自旋到电荷转换效率的影响可能会解决各种文献中的歧义,并基于新兴自旋电子器件的生长过程开辟新的功能。
更新日期:2021-11-26
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