Large Spin Pumping and Inverse Spin Hall Effect in Ta/Py Bilayer Structures

Abstract

Spin mixing conductance at the ferromagnet (FM)/heavy metal (HM) interface is a key parameter to estimate the spin current injection into heavy metal. The electrical detection of such injected spin current in heavy metal is possible via inverse spin Hall effect (ISHE). Herein, a large spin mixing conductance in the range of (4.95−6.52) × 1018 m−2 in Ta/permalloy(Py) bilayer structures is reported. In‐plane angular‐dependent ISHE voltage measurements in Ta/Py samples reveal the dominance of spin pumping voltage component over the other spin rectification contributions. Voltage contribution due to spin pumping and anisotropic magnetoresistance (AMR) increases with the Py thickness due to the enhancement in spin pumping and increase in spin‐dependent scattering, respectively. Anomalous Hall effect (AHE) contribution in Py is found to be relatively small.

Heavy metal deposition temperature tuned spin pumping efficiency control in permalloy/tantalum bilayers

“…A high value of g ↑↓ = 1.45 × 10 18 m −2 has been reported in Py (5 nm)/Ta (20 nm) bilayer having mixed phase of αand β-Ta, with the corresponding value of g ↑↓ = 0.9 × 10 18 m −2 for α-Ta phase [17]. g ↑↓ values of ≈5 × 10 18 m −2 have been reported for bilayers of Ta(10 nm)/ Py (4 nm), where Py is uncapped and α-Ta is the underlayer [18]. These systems show magnetic damping in the range of 8.5 ×10 −3 -1.4 ×10 −2 [17,18].…”

“…Spin pumping strongly depends on the choice of materials used for FM and HM layers [13][14][15][16][17]. Among these material classes permalloy (Py)/tantalum (Ta) bilayer has emerged as one of the promising heterostructure having significant spin pumping efficiency [17][18][19][20][21][22][23]. There has been several studies that have focused on the effect of the thickness variation and structural phase of Py and Ta layers on spin pumping efficiency [17,18,20].…”

“…Among these material classes permalloy (Py)/tantalum (Ta) bilayer has emerged as one of the promising heterostructure having significant spin pumping efficiency [17][18][19][20][21][22][23]. There has been several studies that have focused on the effect of the thickness variation and structural phase of Py and Ta layers on spin pumping efficiency [17,18,20]. Furthermore, the effect of the interface on the spin pumping has been studied by insertion of non-magnetic light transition metal layer of copper between the Py and Ta layers [19].…”

“…Permalloy is an extremely important spintronic material [24,25] having useful properties like high spin density, high magnetic permeability and low magnetic damping [26,27]. On the other hand Ta is being widely explored in FM/HM bilayers due to its high spin-orbit coupling that allows efficient charge current to spin current conversion and vice-versa [14][15][16][17][18][19]. Spin mixing conductance is a key parameter that is used to characterize the spin pumping efficiency.…”

“…g ↑↓ values of ≈5 × 10 18 m −2 have been reported for bilayers of Ta(10 nm)/ Py (4 nm), where Py is uncapped and α-Ta is the underlayer [18]. These systems show magnetic damping in the range of 8.5 ×10 −3 -1.4 ×10 −2 [17,18]. However, smaller magnetic damping is preferred for high frequency applications [32].…”