Abstract
We investigate the Pt thickness dependence of spin–orbit torques (SOTs) in Co/Pt layers grown on single crystalline SrTiO3 and LaAlO3 and amorphous SiO2 substrates. We measure the SOT-induced effective damping-like fields and spin Hall magnetoresistances of the Co/Pt (tPt) samples, where tPt varies from 0.5 to 5.5 nm. We find that the Co/Pt layers grown on the single crystalline substrates show weaker thickness dependence of the SOT than the samples on the SiO2 substrate, which cannot be explained by the conventional bulk spin Hall effect in the Pt layer. This indicates that there is a non-negligible interfacial SOT originating from the Pt/substrate interface, which is more pronounced for thinner Pt. These results provide a way to design SOT material structures with enhanced SOT efficiency by incorporating interfacial SOT.
Highlights
FM/HM bilayer structures: the bulk spin Hall effect (SHE) in the HM layer[27–31] and the interfacial spin–orbit coupling effect.[32–38] For the SHE, an in-plane charge current along the x-direction creates a spin current that flows in the z-direction carrying spin polarization in the y-direction
Since the SHE is of bulk origin, the magnitude of the SHE-based spin–orbit torques (SOTs) depends on the HM thickness; it initially increases with the HM thickness and reaches a saturated value.[5,39–42]
We demonstrate interfacial SOTs originating at the Pt/substrate interface by investigating the Pt thickness dependence of SOTs in Co/Pt bilayers grown on single crystalline SrTiO3 and LaAlO3 and amorphous SiO2 substrates
Summary
FM/HM bilayer structures: the bulk spin Hall effect (SHE) in the HM layer[27–31] and the interfacial spin–orbit coupling effect.[32–38] For the SHE, an in-plane charge current along the x-direction creates a spin current that flows in the z-direction carrying spin polarization in the y-direction. We find that the SOTinduced effective damping-like fields and spin Hall magnetoresistances (SMRs) of the samples with single crystalline substrates show weak dependences on the Pt thickness, revealing non-negligible interfacial spin–orbit coupling effects in the samples.
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