Finite-frequency spin conductance of the interface between a ferro- or ferrimagnetic insulator and a normal metal

The interface between a ferro-/ferrimagnetic insulator and normal metal can support spin currents polarized collinear with perpendicular to the magnetization direction. flow of angular momentum direction ("transverse" current) takes place via torque pumping. ("longitudinal" requires excitation magnons. In this article we extend existing theory longitudinal transport [Bender Tserkovnyak, Phys. Rev. B 91, 140402(R) (2015)] in zero-frequency weak-coupling limit two directions: We calculate conductance non-perturbatively (but low-frequency limit) at finite frequency low transparency). For paradigmatic spintronic material system YIG|Pt, find that non-perturbative effects lead is ca. 40% smaller than perturbative limit, whereas finite-frequency corrections are relevant temperatures < 100 K only, when only few magnon modes thermally occupied.