Spintronics with heavy metals, topological insulators and antiferromagnets

Abstract

The precession of magnetization in a ferromagnet (FM) can transmit pure spin current into an adjacent heavy metal (HM) via spin pumping. This pure spin current gets converted to a charge current due to high spin orbit coupling (SOC) of the HM due to the inverse spin Hall effect (ISHE). I will discuss recent ISHE results on Co2Fe0.4Mn0.6Si/Pt bilayers, where Co2Fe0.4Mn0.6Si is a full Heusler alloy. Damping analysis indicates the presence of significant spin pumping at the interface of Co2Fe0.4Mn0.6Si and Pt [1]. I will also discuss ISHE experiments on some other combinations such as CoFeB/IrO2 and manganite based La0.66Sr0.34MnO3/Pt bilayers [2-3]. Recently AFM materials having high SOC have been found to be a good replacement of HM in spin current based study. We have performed the ISHE study of CoFeB (10 nm)/ AFM (d nm) where we considered various AFM such as Mn2Au, Mn3Ga, IrMn etc. The systematic angle dependent ISHE measurements have been carried out to disentangle the different spin rectification effects viz. anisotropic magnetoresistance and anomalous Hall effect [4-6]. Further I will show the ISHE study on topological insulator (TI)/ferromagnetic Bi2Se3/CoFeB films [7,8]. ISHE experiments have also been performed to demonstrate that TIs are potential candidates to replace HM as they possess high spin-orbit coupling. In the second part of my talk, I will discuss about magnetic skyrmion. Skyrmions in ultrathin films are believed to offer large performance advantages in the development of novel spintronics technologies [9]. Recent studies have shown that skyrmions can be stabilized by interfacial Dzyaloshinskii-Moriya Interaction (iDMI). The controlled nucleation, stabilization, smaller size and efficient motion of skyrmions at room temperature and low magnetic field are the major challenges for R&D purpose. In this context, I will discuss the generation of skyrmions from triangular antidot structure in a ferromagnetic nanotrack using local Oersted field [10]. The dependency of skyrmion size and shape for variable Dzyaloshinskii–Moriya interaction and uniaxial anisotropy will also be discussed [11]. Sometimes the shape of skyrmions is not perfectly circled which is explained by the presence of different local anisotropy energy [12] using micromagnetic simulations. I will discuss the effect of the interlayer exchange interaction on between skyrmion-antiskymion pair [13]. I will also discuss the current induced motion of skyrmions in Pt/CoFeB thin films. The presence of low pinning sites in the Pt/CoFeB thin films helps skyrmions to move with a low threshold current density [14]. Acknowledgement: I like to sincerely thank my group members and collaborators for their hardwork and kind cooperation. I also acknowledge the funding agencies.