Ferromagnetic-ferromagnetic tunneling and the spin filter effect

Tunneling characteristics of a ferromagnetic-antiferromagnetic-ferromagnetic (FM-AFM-FM) thin film tunnel junction were studied in high magnetic fields with a view to investigate magnetic coupling by the tunneling process. Gd2O3, a stable oxide which undergoes antiferromagnetic ordering below about 3.9 K, was chosen as the tunnel barrier between the ferromagnetic electrodes Gd and permalloy. Tunnel characteristics showed as much as 32% decrease in junction resistance in an applied field of 20 T, below 4.2 K. The resistance behavior as a function of H can be explained by two different effects: firstly, the change in tunnel conductance due to change in the relative magnetization of the two FM electrodes in low H; secondly, the spin filter effect in high fields, due to the exchange splitting of the Gd2O3 conduction band.