  Properties are discussed of a ferromagnetic junction of the type "rod
contacting with film". Very high current density of the order of $10^9$
A/cm$^2$ may be achieved in the contact region. We show it can lead to
inversion of population of the spin energy subbands. Spin injection depends
strongly on the direction of the current (forward or backward). We prepared
experimentally a rod-to-film structure and investigated high density current
flowing through it. Current dependent radiation has been observed by means of a
THz receiver. In particular, the radiation becomes different for forward and
backward currents. It shows the radiation includes not only heating but also
non-thermal (spin-injection) effects.
