Current-induced spin polarization on metal surfaces probed by spin-polarized positron beam

Abstract

Current-induced spin polarization (CISP) on the outermost surfaces of Au, Cu, Pt, Pd, Ta, and W nanoscaled films were studied using a spin-polarized positron beam. The Au and Cu surfaces showed no significant CISP. In contrast, the Pt, Pd, Ta, and W films exhibited large CISP (3~15% per input charge current of 105 A/cm2) and the CISP of Ta and W were opposite to those of Pt and Pd. The sign of the CISP obeys the same rule in spin Hall effect suggesting that the spin-orbit coupling is mainly responsible for the CISP. The magnitude of the CISP is explained by the Rashba-Edelstein mechanism rather than the diffusive spin Hall effect. This settles a controversy, that which of these two mechanisms dominates the large CISP on metal surfaces.

Charge-to-Spin Conversion and Spin Diffusion in Bi/Ag Bilayers Observed by Spin-Polarized Positron Beam

“…In 2010, Miron et al detected a current-driven spin torque induced by the REE in Pt(3)/Co(0.6)/A l(1.6)/S i02 [20], In 2011, they observed the perpendicular switching of a single Co ferromagnetic layer in the same sample [21], Our previous report on current-induced spin polarization of six transition metals (Pt, Pd, Au, Cu, Ta, and W) was tentatively explained as the surface spin accumulation due to the REE [10], These samples were also associated with the magnetic layer due to the ferromagnetic property of the nanoscaled Pt and Pd. The validity of the explanation still remains a problem that needs to be experimentally addressed.…”

“…In contrast, ortho-Ps, which decays mostly into three y rays (the decay possibilities into other odd numbers of y rays are negligibly small) with energy ranging between 0 and 511 keV, is distinguishable from two-y events. Inspired by the exciting progress of spintronics in the last decade, a spin-polarized positron beam was developed in order to detect the spin polarization of the outermost surface electrons [9,10],…”

Characterization and Manipulation of Spin Orbit Torque in Magnetic Heterostructures

“…Moreover, the HM crystalline structure is found to largely affect the SHA. When the HM transits into the amorphous phase with a larger resistivity by changing the HM thickness or choosing different substrate or oxidation, the HM/FM bilayers exhibit a larger SHA . Studies have also been carried out by adding nonmagnetic impurities with strong spin‐orbit interactions such as Bi, Ir, Pb, and Pt in Cu to enhance the SHA .…”

Intrinsic magnetoresistance in metal films on ferromagnetic insulators

“…Since the angular dependence is identical, the origin of the recently experimentally discovered "SMR" is still debatable [35]: It can be caused by the bulk spin Hall effects as well as by an interfacial Rashba effect. In principle, different dependences on the NM film thickness may be expected.…”