Temperature dependence of tunnel magnetoresistance

Electric transport through magnetic tunnel junctions (MTJs) has been studie d at various temperatures to gain understanding of the transport mechanisms in such devices. Between 15 and 400 K, MTJs with Al2O3 barriers have been tested at low voltage (barrier height: 2.0-2.1 eV, barrier width: 1.5 nm). For the soft-magnetic electrode a sputtered 1 nm Co/6 nm Fe double layer wa s used. The hard-magnetic electrode is realized with a 1.5 nm Co/1.0 nm Cu/ 1.0 nm Co system. Antiferromagnetic coupling between the two Co layers lead s to a high saturation field. The 1.5 nm Co layer is used as the second ele ctrode of the MTJ. The conductance increases with growing temperature while the tunnel magnetoresistance (TMR) shows a slight decrease. For interpreta tion of the results, the temperature dependence of direct tunneling, of the hopping conductance via trapped states, and of the interface magnetization have to be taken into consideration. The dominant factor for the TMR is pr oportional to 1-BT3/2 and follows the temperature dependence of the interfa ce magnetization. The experimental data allow us to separate transport mech anisms and characterize the junction quality. At room temperature the spin- independent hopping conductance of our junctions is calculated to be less t han 10% of the total conductance. Concerning the magnetic properties, a fer romagnetic orange-peel coupling corresponding to a field of about 4 Oe (0.3 kA/m) was found at 15 K, which decays exponentially with increasing temper ature to less than 0.6 Oe (0.05 kA/m) at 300 K. The coercive field of the s oft layer also shows an exponential decay. (C) 2001 American Institute of P hysics.