Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm Research articles Influence of the two boundaries of the Pt layer on spin current transportation by spin Hall magnetoresistance Zhiwen Dai, Xiufeng Huang ⁎ , Dongchao Yang, Lizhi Yi, Fengyu Wu, Hongguang Piao, Liqing Pan ⁎ Research Institute for Magnetoelectronics & Weak Magnetic-field Detection, College of Science, China Three Gorges of University, Yichang 443002, China ARTICLE INFO Keywords: Spin Hall magnetoresistance Spin Hall effects Spin current absorption Anisotropic magnetoresistance Spin current transportation ABSTRACT The spin Hall magnetoresistance effects (SMR) in four heterostructures consist of different boundaries of Pt layer has been investigated. The result in this work shows that the two boundaries of Pt layer in all heterostructures both influence the spin current absorption and reflection. The Pt/air interface would weaken the spin current absorption at the Co 2 FeSi/Pt interface on the other side of the Pt layer. On the contrary, the Pt/MgO(0 0 1) interface could boost the spin current absorption strongly at the Co 2 FeSi/Pt interface on the other side of the Pt layer. And this promotion effect is much stronger than the Co 2 FeSi/Pt interface on the spin current absorption at the other Co 2 FeSi/Pt interface. The MgO capping layer may avoid anisotropic magnetoresistance (AMR) induced SMR ratio decreasing at low temperature. This study provides a new way for modulating spin current absorption at the FM/HM interface. 1. Introduction The generation, transportation and detection of pure spin current are central issues in spintronics. There are many physical phenomena are related to pure spin current, such as spin Hall effect (SHE) [1–3], inverse spin Hall effect (ISHE) [4,5], spin pumping [6,7], spin Seebeck effect (SSE) [8,9], spin-dependent thermoelectric effect [10,11], spin Peltier effect (SPE) [12,13], and spin Hall magnetoresistance (SMR) [14–16]. All these phenomena involve spin current transportation in heavy metal (HM) layer contacted with ferromagnetic (FM) layer. The FM layer can be insulator, semiconductor, or metal [17–19]. Strong spin-orbit coupling exists in the interface between the HM layer and the FM one. Many factors affect the spin current absorption and reflection at the FM/HM interface. The spin Hall angle which represents the strength of the spin-orbit coupling is a dominant one [20]. The property of the FM/HM interface plays an important role as well [21]. Recent study shows that spatial distribution of spin current is more compli- cated in FM/HM based multilayer structure compared to FM/HM single bilayer structure [22]. Several spin current related phenomena in HM/ FM based multilayer structures such as SSE and SPE indicate that the magnitude of the spin current in the middle layer is largest. It becomes smaller and smaller when the spin currents distribute in the layer away from the middle one [23]. Spin Hall magnetoresistive effect which is the collective effect of SHE and ISHE attracts great interest of people in recent years. Therefore, SMR can be used as a practical method for the study of spin current generation, propagation and detection. The latest research [24–26] on the SMR in YIG/antiferromagnetic insulator (AFI)/Pt and AFI/Pt heterostructures indicates that spin mixing conductance could be enhanced significantly when the thickness of the AFI increases from zero to several nanometers. Spin flip may occur at the AFI/Pt interface when the AFI exchanges coupled with YIG at low temperature. These researches show that magnetic microstructure at the interface influence the SMR significantly. The spin current can be generated in the HM layer connected with FM due to SOC. However, many factors affect the spin current absorption and reflection at the FM/HM interface. The HM layer with spin current transporting in it has two boundaries around it. In addition, the spin diffusion length in the HM layer is only several nanometers. It is not clear that apart from the FM/HM boundary, whether another boundary of the HM layer participates in the spin current transportation. In this paper, we investigate the two boundaries of the Pt layer on spin current transportation by using spin Hall magnetoresistance. We report the SMR in different kinds of heterostructures with the Pt layer having different boundaries. The work shows that different boundaries of the Pt layer influence the spin current absorption significantly. This study provides a new way for modulating spin current absorption from HM layer to the FM layer. 2. Experimental In this experiment, four heterostructures, from bottom to top, MgO https://doi.org/10.1016/j.jmmm.2018.06.060 Received 2 May 2018; Received in revised form 12 June 2018; Accepted 19 June 2018 ⁎ Corresponding author. E-mail addresses: xiufenghuang@ctgu.edu.cn (X. Huang), lpan@ctgu.edu.cn (L. Pan). Journal of Magnetism and Magnetic Materials 465 (2018) 585–589 Available online 20 June 2018 0304-8853/ © 2018 Elsevier B.V. All rights reserved. T