Dependence of spin-pumping spin Hall effect measurements on layer thicknesses and stacking order

Vlaminck, Vincent; Pearson, John; Bader, S. D.; Hoffmann, A.

doi:10.1103/physrevb.88.064414

Cited by 118 publications

(108 citation statements)

References 42 publications

(51 reference statements)

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“…Accurate determination of τ s could also help to identify the spin relaxation mechanisms [12]. Though θ SH and l s have been measured by spin pumping [13][14][15][16][17] In fact, spin injection experiments in nonlocal spin valves [29][30][31][32][33][34][35] and 3-terminal geometries [36][37][38][39][40] are both powerful tools in measuring τ s in metals and semiconductors. In these experiments, ferromagnetic layer (FM)/tunnel barrier/nonmagnetic layer (NM) junctions are adopted to both inject a non-equilibrium spin accumulation and simultaneously determine their magnitude.…”

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“…Accurate determination of τ s could also help to identify the spin relaxation mechanisms [12]. Though θ SH and l s have been measured by spin pumping [13][14][15][16][17] and 2nd harmonic Hall measurement [18][19][20], τ s of Pt and Ta is rarely reported. In principle, τ s = l 2 s /D, with D being the diffusion constant, which is also difficult to determine independently.…”

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Determination of spin relaxation times in heavy metals via second-harmonic spin injection magnetoresistance

et al. 2017

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In tunnel junctions between ferromagnets and heavy elements with strong spin orbit coupling the magnetoresistance is often dominated by tunneling anisotropic magnetoresistance (TAMR). This makes conventional DC spin injection techniques impractical for determining the spin relaxation time (τs). Here, we show that this obstacle for measurements of τs can be overcome by 2nd harmonic spin-injection-magnetoresistance (SIMR). In the 2nd harmonic signal the SIMR is comparable in magnitude to TAMR, thus enabling Hanle-induced SIMR as a powerful tool to directly determine τs. Using this approach we determined the spin relaxation time of Pt and Ta and their temperature dependences. The spin relaxation in Pt seems to be governed by Elliott-Yafet mechanism due to a constant resistivity×spin relaxation time product over a wide temperature range.PACS numbers: 72.25. Rb, 72.25.Ba, 73.50.Bk, 73.40.Rw The large applied potential of spin-orbit-torques for magnetic random access memory has stimulated intensive interest in investigating spin orbit coupling (SOC) in heavy metals such as Pt and Ta [1][2][3][4][5][6][7][8][9][10][11]. Their spin Hall angle (θ SH ), spin diffusion length (l s ) and spin relaxation time (τ s ), which influence switching efficiency are important parameters for determining their effectiveness, but especially the latter two are experimentally hard to assess. Accurate determination of τ s could also help to identify the spin relaxation mechanisms [12]. Though θ SH and l s have been measured by spin pumping [13][14][15][16][17] In fact, spin injection experiments in nonlocal spin valves [29][30][31][32][33][34][35] and 3-terminal geometries [36][37][38][39][40] are both powerful tools in measuring τ s in metals and semiconductors. In these experiments, ferromagnetic layer (FM)/tunnel barrier/nonmagnetic layer (NM) junctions are adopted to both inject a non-equilibrium spin accumulation and simultaneously determine their magnitude. These measurement were used to determine spin relaxation times in a wide variety of materials, e.g., τ s,Si =55 -285 ps for heavily doped silicon [40]; τ s,Graphene > 1 ns for graphene/BN [41]; τ s,Al =110 ps for aluminum [29], τ s,Cu =22 ps for copper [42] and τ s,Au =45 ps for gold [32].However, it is impractical to apply these spin injection experiments to measure τ s in heavy metals with strong SOC for at least two reasons. First, l s in this case is so short (about several nanometers) that the preparation of nonlocal spin valves with comparable dimensions is beyond current lithography capabilities. Second, the real contact resistance is r = r C + r SI , where r SI and r C are the contact resistance induced by spin injection (SI) and the original contact resistance without r SI , respectively. Here r SI equals to r N r C /(r N +r C ) and the spin resistance in the NM layer r N is defined as ρ N l sN . ρ N and l sN are the resistivity and spin relaxation length of NM, respectively. For this discussion we ignore the influence of spin resistance in FM on r SI due to...

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Determination of spin relaxation times in heavy metals via second-harmonic spin injection magnetoresistance

et al. 2017

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“…As a result, both SHE and ISHE in Au have been extensively studied by various techniques. [20][21][22][23][24][25][26][27][28] These studies have reported values of θ SH for Au between 0.25% (0.0025) and 11% (0.11). This broad range of measured values can be attributed to the use of varying experimental techniques and to Au layer thicknesses.…”

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Thickness dependence of spin Hall angle of Au grown onY3Fe5O12epitaxial films

et al. 2016

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We measure the spin Hall angle in Au layers of 5 to 100 nm thicknesses by spin pumping from Y 3 Fe 5 O 12 epitaxial films grown by ultrahigh vacuum, off-axis sputtering. We observe a striking increase in the spin Hall angle for Au layers thinner than the measured spin diffusion length of 12.6 nm. In particular, the 5 nm Au layer shows a large spin Hall angle of 0.087, compared to those of 0.016 and 0.017 for the 50 and 100 nm Au layers, respectively, suggesting that the top surface plays a dominant role in spin Hall physics when the spin current is able to reach it. Other spin pumping related parameters, including Gilbert damping enhancement, interfacial spin mixing conductance, and spin current are also determined for Au layers of various thicknesses.Given the pervasive role ultrathin films in electrical and spin transport applications, this result emphasizes the importance of considering the impact of the top surface and reveals the possibility of tuning critical spin parameters by film thickness. PACS: 72.25.Ba, 76.50.+g, 72.25.Mk, 75.70.Ak 2The spin Hall effect (SHE) and its reciprocal process, the inverse spin Hall effect (ISHE), have generated intense interest in recent years as a means of producing, manipulating, and detecting spin currents in nonmagnetic materials, opening new routes to spin-based electronic applications.1-13 The ability to convert an unpolarized electrical current into a spin current can be quantitatively described by the spin Hall angle (θ SH ).14,15 θ SH is a material-specific quantity that arises from spin-orbit coupling (SOC). Its magnitude and sign are primarily determined by atomic number, and for transition metals, by the d-orbital filling. [16][17][18][19] Au is a transition metal with a large atomic number of 79, which should lead to strong SOC and hence a large θ SH . As a result, both SHE and ISHE in Au have been extensively studied by various techniques. 20-28These studies have reported values of θ SH for Au between 0.25% (0.0025) and 11% (0.11 during film growth and the substrate rotates at 10 degrees/sec to achieve optimal film uniformity.A radio-frequency power of 60 W is used for YIG sputtering, which gives a deposition rate of 0.51 nm/min. The Au is grown in-situ on the YIG film at room temperature by off-axis DC sputtering at a deposition rate of 2.24 nm/min. The crystalline quality of the YIG films and YIG/Au bilayers are examined by X-ray diffraction (XRD) and X-ray reflectivity (XRR) using a 3 Bruker D8 Discover high-resolution triple-axis X-ray diffractometer, and scanning transmission electron microscopy (STEM) using an FEI probe-corrected Titan 3 80-300 S/TEM. where e is the electron charge, σ Au is the Au conductivity, λ SD is the spin diffusion length in Au, is the effective interfacial spin mixing conductance, L is the sample length, P = 1.21 is a factor due to the ellipticity of magnetization precession, 5 γ is the gyromagnetic ratio, h rf = 0.25Oe is the rf magnetic field in the EPR cavity at P rf = 200 mW, and α is the Gilbert damping constant of ...

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“…We define a parameter W ISHE , which represents the weight of the symmetric component (ISHE). W ISHE can be further expressed in the form of W ISHE = 1/(1+V AMR /V ISHE ), and the ratio of the two components can be written as [27]:…”

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