Sriram K, Pala Jay, Paikaray Bibekananda, Haldar Arabinda, Murapaka Chandrasekhar
Department of Materials Science and Metallurgical Engineering, Indian Institute of Technology Hyderabad, Kandi-502284, Telangana, India.
Department of Physics, Indian Institute of Technology Hyderabad, Kandi-502284, Telangana, India.
Nanoscale. 2021 Dec 13;13(47):19985-19992. doi: 10.1039/d1nr06007d.
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 = -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.
重金属 - 铁磁体双层结构因其电荷到自旋的相互转换而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）种子层对钽（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种子层上的Ta的晶相强烈依赖于种子层的厚度。我们观察到随着Py种子层厚度的增加，Ta从α - Ta相转变为（α + β）- Ta相。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中的自旋混合电导相对较高。α - Ta和（α + β）- Ta的自旋霍尔角是通过逆自旋霍尔效应（ISHE）测量获得的。（α + β）- Ta的自旋霍尔角估计为 = -0.15 ± 0.009，相对高于α - Ta的自旋霍尔角。我们将Ta的相与其种子层相关联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模糊之处，并基于新兴自旋电子器件的生长过程开辟新的功能。
