We report a giant spin-orbit torque (SOT) induced by spin Hall effect (SHE) in amorphous Pt(P) alloys, which is confirmed by magnetization switching and spin torque-ferromagnetic resonance measurements. Pt(P) is fabricated by ion-implantation technique using energies from 10 to 30 keV with doses ranging from 2.5 × 1016 to 10 × 1016 ions/cm2. The P-ion implantation process causes distortion and defects in the fcc structure of the as-deposited Pt layer and changes it to an amorphous structure as the accelerating energy as well as the dose increases, leading to a decrease in the electrical conductivity. However, we can obtain a higher spin Hall conductivity, <InlineEquation ID="IEq1"> <EquationSource Format="TEX">${\sigma }_{{\rm{xy}}}^{{\rm{SH}}}$</EquationSource> <EquationSource Format="MATHML"><math> <msubsup> <mrow> <mi>σ</mi> </mrow> <mrow> <mi mathvariant="normal">xy</mi> </mrow> <mrow> <mi mathvariant="normal">SH</mi> </mrow> </msubsup> </math></EquationSource> </InlineEquation> of <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$3.62\times {10}^{3}\frac{\hslash }{2e}{\Omega }^{-1}{\mathrm{cm}}^{-1}$</EquationSource> <EquationSource Format="MATHML"><math display="inline"> <mrow> <mn>3.62</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mn>3</mn> </msup> <mfrac> <mrow> <mi>ℏ</mi> </mrow> <mrow> <mn>2</mn> <mi>e</mi> </mrow> </mfrac> <msup> <mrow> <mi>Ω</mi> </mrow> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> <msup> <mrow> <mi>cm</mi> </mrow> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> for Pt(P) as compared to that of <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$1.03\times {10}^{3}\frac{\hslash }{2e}{\Omega }^{-1}{\mathrm{cm}}^{-1}$</EquationSource> <EquationSource Format="MATHML"><math> <mrow> <mn>1.03</mn> <mo>×</mo> <msup> <mrow> <mn>10</mn> </mrow> <mn>3</mn> </msup> <mfrac> <mrow> <mi>ℏ</mi> </mrow> <mrow> <mn>2</mn> <mi>e</mi> </mrow> </mfrac> <msup> <mrow> <mi>Ω</mi> </mrow> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> <msup> <mrow> <mi>cm</mi> </mrow> <mrow> <mo>−</mo> <mn>1</mn> </mrow> </msup> </mrow> </math></EquationSource> </InlineEquation> for pure Pt. The spin Hall efficiency, <InlineEquation ID="IEq4"> <EquationSource Format="TEX">${\theta }_{{\rm{SH}}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi mathvariant="normal">SH</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> is drastically increased up to 1.17 for Pt(P) with 30 keV energy and dose of 7.5 × 1016 ions/cm2. We also observe a significant reduction in the critical switching current density, <InlineEquation ID="IEq5"> <EquationSource Format="TEX">${J}_{{\rm{sw}}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mi>J</mi> </mrow> <mrow> <mi mathvariant="normal">sw</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> of the SOT magnetization switching from 1.5 × 1011 A/m2 for pure Pt to 3.0 × 1010 A/m2 for Pt(P). Such a giant SHE can reduce the power consumption to control the magnetization by using SOT, and therefore our findings may provide an alternate path to enhance <InlineEquation ID="IEq6"> <EquationSource Format="TEX">${\theta }_{{\rm{SH}}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mi>θ</mi> </mrow> <mrow> <mi mathvariant="normal">SH</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> by using amorphous materials with a variety of elements, beyond crystalline solids.

Giant spin-orbit torque induced by spin Hall effect in amorphous Pt(P) alloys

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2025年4月11日

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Utkarsh Shashank,
Takafumi Tomoda,
Arun Jacob Mathew,
Garima Vashisht,
Koki Imai,
Yu Kusaba,
Chung-Li Dong,
Chi-Liang Chen,
Yoichi Horibe,
Manabu Ishimaru,
Hiroyuki Awano,
Hironori Asada,
Yasuhiro Fukuma

摘要

We report a giant spin-orbit torque (SOT) induced by spin Hall effect (SHE) in amorphous Pt(P) alloys, which is confirmed by magnetization switching and spin torque-ferromagnetic resonance measurements. Pt(P) is fabricated by ion-implantation technique using energies from 10 to 30 keV with doses ranging from 2.5 × 10¹⁶ to 10 × 10¹⁶ ions/cm². The P-ion implantation process causes distortion and defects in the fcc structure of the as-deposited Pt layer and changes it to an amorphous structure as the accelerating energy as well as the dose increases, leading to a decrease in the electrical conductivity. However, we can obtain a higher spin Hall conductivity, ${\sigma }_{{\rm{xy}}}^{{\rm{SH}}}$ $σ_{xy}^{SH}$ of $3.62\times {10}^{3}\frac{\hslash }{2e}{\Omega }^{-1}{\mathrm{cm}}^{-1}$ $3.62 \times 10^{3} \frac{ℏ}{2 e} Ω^{- 1} {cm}^{- 1}$ for Pt(P) as compared to that of $1.03\times {10}^{3}\frac{\hslash }{2e}{\Omega }^{-1}{\mathrm{cm}}^{-1}$ $1.03 \times 10^{3} \frac{ℏ}{2 e} Ω^{- 1} {cm}^{- 1}$ for pure Pt. The spin Hall efficiency, ${\theta }_{{\rm{SH}}}$ $θ_{SH}$ is drastically increased up to 1.17 for Pt(P) with 30 keV energy and dose of 7.5 × 10¹⁶ ions/cm². We also observe a significant reduction in the critical switching current density, ${J}_{{\rm{sw}}}$ $J_{sw}$ of the SOT magnetization switching from 1.5 × 10¹¹ A/m² for pure Pt to 3.0 × 10¹⁰ A/m² for Pt(P). Such a giant SHE can reduce the power consumption to control the magnetization by using SOT, and therefore our findings may provide an alternate path to enhance ${\theta }_{{\rm{SH}}}$ $θ_{SH}$ by using amorphous materials with a variety of elements, beyond crystalline solids.