Quantum well oscillations in giant magnetoresistance and conductance with ferromagnetic free layer thickness in spin-valve structures with inverted [Co/Pt]n/Co reference layer

We present a study on the conductance and giant magnetoresistance effect in Co/Cu/(Co/Pt)4/Co/IrMn spin valves, where the inverted [Co/Pt]4/Co reference layer and the Co free layer exhibit fcc (111) and hcp (100) orientations along the z-axis. The term ’inverted’ refers to sub-nanometer thickness for both Co and Pt layers, with Pt having a smaller thickness compared to Co. By varying the thickness of the Co free layer from 0.3 to 3.2 nm, we observe oscillations in both in-plane and perpendicular conductance as well as giant magnetoresistance, displaying a superposition of two periods (2.6 and 3.7 monolayers of the Co free layer). First-principle calculations suggest that these oscillations can be attributed to quantum well states occurring in minority channels between fcc Co(111) and hcp Co(100) within multilayered structures of Co/Cu(111)/Co, thereby providing an opportunity for precise manipulation of spin electrons within sub-nanometer scale textured layers.