Stimulated emission of radiation using spin-population inversion in   metals: a spin-laser
  Arrays of 10 nm-diameter point contacts of exchange-coupled spin-majority/spin-minority ferromagnetic metals, integrated into infrared-terahertz range photon resonators, are fabricated and measured electrically and optically. Giant, threshold-type electronic excitations under high-current pumping of the devices are observed as abrupt but reversible steps in device resistance, in many cases in access of 100%, which correlate with optical emission from the devices. The results are interpreted as due to stimulated spin-flip electron-photon relaxation in the system. 
V. Korenivski, A. Iovan, A. Kadigrobov, and R. I. Shekhter
cond-mat.mes-hall quant-ph