Relationship between tunnel magnetoresistance and magnetic layer structure in EuO-based tunnel junctions investigated using polarized neutron reflectivity

This paper presents a study of the depth-dependent magnetic structure of a EuO magnetic tunnel junction having a Gd electrode, Si/Cu/EuO/Gd/Al. Related samples that are patterned exhibit large tunneling magnetoresistance as high as 280%. Though Gd has a much higher coercivity than EuO in bulk, magnetometry reveals no steps in the hysteresis loop as expected for a true antiparallel alignment of the EuO and Gd layer magnetizations. Using polarized neutron reflectometry to measure the structural and field-dependent magnetic depth profile at 5 K, we determine that the Gd and EuO layers have similar coercivities and that the Gd layer exhibits an anomalously small magnetization at all fields. Polarized neutron reflectometry results also suggest that the chemical density of the Gd layer is not that of bulk Gd. The differences of the structural and magnetic behavior of the Gd layer relative to bulk may be the key in optimizing the tunnel magnetoresistance in these samples.