Metallic superlattices revisited for spintronics

Takanashi, Koki

The recent progress of spintronics shows new developments such as spin orbitronics, antiferromagnetic spintronics, and spin caloritronics. For these emerging research areas, the importance of interfaces has attracted much attention because of the possible enhancement of spin-orbit interaction at interfaces. The metallic superlattice as an assembly of interfaces is useful for the systematic study of interface effects. In our group, metallic superlattices have been studied from the viewpoint of modern spintronics: For spin orbitronics, the relationship between PMA and spin orbit torque (SOT) has been investigated in symmetric Pt/Co/Pt and Pd/Co/Pd, and asymmetric Pd/Co/Pt layered systems, revealing a clear correlation between the field-like SOT and the Rashba-type contribution to PMA induced by broken inversion symmetry. For antiferromagnetic spintronics, Cu-Ir alloy has been found to show a large spin Hall effect with definite antiferromagnetic IEC induced when it is sandwiched by two ferromagnetic layers. The magnetization switching process induced by SOT has also been investigated in antiferromagnetically-coupled layered systems Pt/Co/Ir/Co/Pt, using domain structure observation and a numerical calculation based on a macrospin model. Furthermore, large antisymmetric IEC in addition to symmetric IEC has been observed, and the influence of the antisymmetric IEC on magnetization switching has been discussed. For spin caloritronics, the enhancement of anomalous Nernst effect has been confirmed in several superlattices with ferromagnetic and nonmagnetic metals alternated. Furthermore, the enhanced anomalous Nernst effect and suppressed thermal conductivity have been demonstrated in metallic superlattices.