Nonlocal magnon transconductance in extended magnetic insulating films. I. Spin diode effect

Combining the nonlinear properties of ferromagnets with the spin-transfer effect promises to realize a ``perfect'' diode with pure spin conductors. Practical implementations are nonlocal devices that emit and collect magnons between two parallel electrodes on a magnetic insulator. A diode-like current-voltage characteristic appears, which is attributed to nonlinear enhancement of the low-energy magnon population. However, its amplitude is rather small and can be explained by the strong enhancement of magnon-magnon scattering near the diode threshold. This suggests conductance by a magnon fluid instead of a frictionless condensate.