Local spin current probe of the global electrodynamics of ultrathin magnetic heterostructure electrofoils

Spin current - the flow of angular momentum mediated by electrons - is a unique probe of non-trivial phases in ultrathin magnetic heterostructures. Electron spin, however, is highly sensitive to nearby electric and magnetic fields; thus, it is important to characterize nonlocal effects in spintronic devices. The high spin-orbit coupling of platinum in conjunction with ferrimagnetic insulator Yttrium Iron Garnet (YIG) provides an optimal platform for evaluating spin current as a robust probe. Here, we demonstrate the first technique capable of imaging the electric field using spin current as a local probe in Pt/YIG magnetic heterostructures. An imaging laser produces a localized thermal gradient that generates an out-of-plane spin current. In the Pt layer, this spin current scatters electrons in-plane and away from the external magnetic field, producing moving charges which interact with the local electric flux to generate a global voltage that we image in space. Electrofoil Pt/YIG devices, made with airfoil-shaped cutouts, are used to study several subtle nonlocal geometric effects, all of which are well described by the Shockley-Ramo theorem.