Optimizing the spin Hall effect in Pt-based binary alloys

Abstract

We present multicode calculations for the spin Hall effect in binary Pt-based alloys, where we explore the viability of alloying the archetype spin Hall material Pt with a large set of metals [Al, Ag, Au, Cu, Hf (hcp), Hf (fcc), Ir, Pd] in order to optimize the charge to spin current conversion for practical applications. To capture intrinsic and extrinsic mechanisms in material-specific calculations, we employ different first-principles codes based on density functional theory in the framework of Green's-function-based multiple scattering approaches. Capturing the transport properties within the relativistic and fully quantum mechanical Kubo-Bastin formalism as well as the semiclassical Boltzmann approach allows for a better understanding of the microscopic physics as well as a larger set of reliable data for the key transport parameters. If available, we compare our results to experimental data, where we generally find good agreement. As we access the full concentration range, we are able to identify the optimal doping regime, which will depend on the binary alloy but generally falls within a region of 60–90 at.% of Pt. When including the unavoidable experimental residual resistivities, the maximum spin Hall angle that we identified is <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:mspace width="0.16em"/><a:mn>13</a:mn><a:mo>%</a:mo></a:mrow></a:math> in <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:msub><c:mi>Al</c:mi><c:mrow><c:mn>0.2</c:mn></c:mrow></c:msub><c:msub><c:mi>Pt</c:mi><c:mrow><c:mn>0.8</c:mn></c:mrow></c:msub></c:mrow></c:math> and <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:msub><d:mi>Hf</d:mi><d:mrow><d:mn>0.1</d:mn></d:mrow></d:msub><d:msub><d:mi>Pt</d:mi><d:mrow><d:mn>0.9</d:mn></d:mrow></d:msub></d:mrow></d:math>, which is comparable to the best spin Hall angles experimentally found in good metal systems. The longitudinal resistivities in this regime go beyond <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"><e:mrow><e:mn>70</e:mn><e:mspace width="0.16em"/><e:mi>µ</e:mi><e:mi mathvariant="normal">Ω</e:mi></e:mrow></e:math> cm, which is compatible with metallic-based magnetic random access memory devices. Published by the American Physical Society 2024

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