Spin-to-Charge Conversion in All-Oxide La_2/3Sr_1/3MnO₃/SrIrO₃ Heterostructures

Abstract

Spin injection and spin−charge conversion processes in all-oxide La 2/3 Sr 1/3 MnO 3 /SrIrO 3 (LSMO/SIO) heterostructures with different SIO layer thickness and interfacial features have been studied. Ferromagnetic resonance (FMR) technique has been used to generate pure spin currents by spin pumping (SP) in ferromagnetic (FM) half-metallic LSMO. The change of the resonance linewidth in bare LSMO layers and LSMO/SIO heterostructures suggests a successful spin injection into the SIO layers. However, low values of the spin mixing conductance, compared to more traditional permalloy (Py)/Pt or yttrium iron garnet (YIG)/Pt systems, are found. A thorough analysis of the interfaces by high-resolution scanning transmission electron microscopy (HR-STEM) imaging suggests that they are structurally clean and atomic sharp, but a compositional analysis by energy-dispersive X-ray spectroscopy (EDS) reveals the interdiffusion of La, Ir, and Mn atomic species in the first atomic layers close to the interface. Inverse spin Hall effect (ISHE) measurements evidence that interfacial features play a very relevant role in controlling the effectiveness of the spin injection process and low transversal ISHE voltage signals are detected. In addition, it is found that larger voltage signals are detected for the lowest SIO layer thickness highlighting the role of the spin diffusion length (λ sd )/SIO layer thickness ratio. The values of ISHE voltage are rather low but allow us to determine the spin Hall angle of SIO (θ SH ≈ 1.12% at T = 250 K), which is remarkably similar to that obtained for the well-known Py/Pt system, therefore suggesting that SIO could be a promising spin-Hall material.

Evaluation of Sputtering Processes in Strontium Iridate Thin Films

“…Reciprocal space maps (not shown, see Ref. [9]) confirmed that, in the range of thickness studied in this work, SIO films are always fully strained with the STO underlying substrate (a STO = 0.3905 nm) [9,10,20]. The observed cell parameters point towards an elastic behavior solely attributed to the in-plane compressive strain imposed by the substrate, consistent with prior reports [9].…”

“…Furthermore, the literature about unexpected SIO-113 electronic properties, including strange metallicity [11,12] or the anomalous or topological Hall effect, is large [13][14][15]. On the other hand, due to its large spin-orbit coupling, it has also been employed in heterostructures for spin torque or spin-to-charge conversion experiments [16][17][18][19][20].…”

Tuning Stoichiometry for Enhanced Spin‐Charge Interconversion in Transition Metal Oxides

“…Therefore, in a simplified model, the expected V ISHE in the bilayer would be proportional to 𝜉 and the bilayer resistance (R). [6,[59][60][61] We find that the relative increase of R is smaller than the enhancement of V ISHE from 0.49 to 1.21 μV, revealing the increased 𝜉 that is consistent with ST-FMR and SHH results. Furthermore, we show that the V ISHE is further enhanced to 1.49 μV by inserting a thin layer (2 nm) of antiferromagnetic insulator LaFeO 3 (LFO) between La 0.66 Sr 0.33 MnO 3 and SrIr 1-x O 3 , which is likely attributed to the suppression of the shunting effect and may also be contributed by the enhancement of interfacial transparency.…”

“…The ferromagnetic La 0.66 Sr 0.33 MnO 3 was opted as the spin‐current source layer due to the minimal spin rectification effects as compared to the highly conductive Py. [ 59 ] Considering the lattice mismatch, SrTiO 3 substrate was used to grow La 0.66 Sr 0.33 MnO 3, showing excellent ferromagnetic properties at room temperature (Figure S8, Supporting Information). We further demonstrate that SrIrO 3 on SrTiO 3 substrates also shows the similar structure changes by reducing the growth oxygen partial pressure, further suggesting that the control of Ir vacancies by growth is universal on different substrates (Figure S9, Supporting Information).…”

“…To assess the role of cation vacancy, we conducted spin pumping measurement [24,58,59] using all-oxide heterostructures comprised of La 0.66 Sr 0.33 MnO 3 (LSMO, 15 nm) and SrIr 1-x O 3 (SIO, 5 nm). The ferromagnetic La 0.66 Sr 0.33 MnO 3 was opted as the spin-current source layer due to the minimal spin rectification effects as compared to the highly conductive Py.…”