[23a-B201-1~12] 10.4 Spintronics in semiconductor, topological material, superconductor, and multiferroics

▼ [23a-B201-12] Fabrication and characterization of polycrystalline Mn₃Sn/Ta structures

〇(D)Takumi Matsuo¹, Tomoya Higo^1,2,3,4, Hanshen Tsai^1,2,3, Daisuke Nishio-Hamane², Satoru Nakatsuji^1,2,3,4,5 (1.Dept. of Phys., Univ. of Tokyo, 2.ISSP, Univ. of Tokyo, 3.JST-CREST, 4.Trans-Quantum Sci. Inst., 5.Johns Hopkins U.)

Keywords:Topological material, Weyl antiferromagnet, Interface

Time-reversal symmetry (TRS) breaking antiferromagnets (AFMs) are recently a topic of interest due to their large responses such as the anomalous Hall effect (AHE) and the anomalous Nernst effect that do not scale with their vanishingly small net magnetization. In the case of the noncollinear Weyl AFM Mn₃Sn, these responses can be attributed to the ordering of the cluster magnetic octupole, an order parameter that encapsulates the TRS-breaking spin structure. The magnetic octupole corresponds to the orientation of a pair of Weyl points in momentum space. In thin films of Mn₃Sn, the octupole can be switched by a spin current injected from a neighboring layer with strong spin-orbit coupling, most commonly a heavy metal (HM). To study surface-dependent effects in Mn₃Sn such as spin-orbit torque, thinner films and smoother interfaces with other materials are desired.
Our work focuses on polycrystalline Mn₃Sn/Ta bilayers, where Ta caps the Mn₃Sn layer due to the prospect of using it as a spin source. We show that the immiscibility of these two materials allows for greater flexibility in the fabrication process than when HM = Pt, W. Transmission electron microscopy and atomic force microscope reveal that the resultant films yield a smoother Mn₃Sn/HM interface (RMS ~ 0.5 nm) compared to conventionally prepared polycrystalline films. Furthermore, where previous works report Mn₃Sn films with thicknesses above 30 nm, large anomalous Hall conductivity comparable to that of bulk crystals was retained in our Mn₃Sn layers as thin as 20 nm.