Electron-Magnon Effects in Ferromagnetic Junctions

Abstract

We have investigated the effect of magnons on the tunneling characteristics of a metal ($A$)-oxide of $A$-metal ($B$) junction in which metal $B$ is ferromagnetic and metal $A$ is a simple metal. The magnons influence the tunneling conductance in two ways: (1) They produce conduction-electron self-energy effects which modify the tunneling density of states, and (2) they give rise to an additional magnon-assisted inelastic tunneling channel. The calculations were performed using an s-f model. The self-energy corrections give rise to two symmetric peaks located at an energy at which the magnon becomes degenerate with the spin-flip excitations of the conduction band. Using parameters appropriate for Gd, this effect is of the order of 1%. The magnon-assisted tunneling produces an additional conductance whose characteristic depends on whether the barrier is diffuse or specular. This additional conductance contains both an even and an odd contribution. The magnitude of the odd part depends on the ratio of the characteristic magnon energy to the barrier height. A critique of the momentum and energy dependence of the tunneling matrix elements is given in connection with the above calculations.