Giant magnetoresistance and tunnel magnetoresistance effects in FeCoGd-based spin valves and magnetic tunnel Junctions

摘要

Giant magnetoresistance (GMR) and tunnel magnetoresistance (TMR) were studied in spin valves of FeCo/Cu/(FeCo)_(1-x)-Gd_x and magnetic tunnel junctions of FeCo/AlO/(FeCo)_(1-x)Gd_x, respectively. When the FeCoGd layer is thick enough, both GMR and TMR ratios change their signs from positive to negative at the compensation composition with 0.293< =x_0<=0.337 as the Gd content is increased. This scenario is originated from a competition of rare-earth and transition-metal spins in FeCoGd layers with antiferromagnetic coupling. Accordingly, it is deduced that in the FeCoGd layer the spin polarizations P_N of electrons at the Fermi level and tunneling spin polarization P_(TSP) are negative and positive for x x_0.