Abstract
The spin–orbit torque, a torque induced by a charge current flowing through the heavy-metal-conducting layer with strong spin–orbit interactions, provides an efficient way to control the magnetization direction in heavy-metal/ferromagnet nanostructures, required for applications in the emergent magnetic technologies like random access memories, high-frequency nano-oscillators, or bioinspired neuromorphic computations. We study the interface properties, magnetization dynamics, magnetostatic features, and spin–orbit interactions within the multilayer system Ti(2)/Co(1)/Pt(0–4)/Co(1)/MgO(2)/Ti(2) (thicknesses in nanometers) patterned by optical lithography on micrometer-sized bars. In the investigated devices, Pt is used as a source of the spin current and as a nonmagnetic spacer with variable thickness, which enables the magnitude of the interlayer ferromagnetic exchange coupling to be effectively tuned. We also find the Pt thickness-dependent changes in magnetic anisotropies, magnetoresistances, effective Hall angles, and, eventually, spin–orbit torque fields at interfaces. The experimental findings are supported by the relevant interface structure-related simulations, micromagnetic, macrospin, as well as the spin drift-diffusion models. Finally, the contribution of the spin–orbital Edelstein–Rashba interfacial fields is also briefly discussed in the analysis.
Highlights
The magnetic multilayer structures consisting of thin ferromagnetic (F) layers and nonmagnetic spacers are known to exhibit plenty of phenomena, among which one can find those extensively studied for the last decades like anisotropic, giant and tunneling magnetoresistance or spin-transfer torque effect (STT),[1,2] and recently, current-driven spin−orbit torque (SOT) magnetization switching.[3]
We show that anisotropies and the interlayer exchange coupling (IEC) strongly depend on the Pt thickness, for Pt layer thicknesses less than 2 nm
We were able to determine four ranges of Pt thickness where the trilayer reveals different static and dynamic behaviors correlated with the strength of coupling: region I, region II (Co magnetizations are both perpendicular to the plane), region III, and, region IV
Summary
The magnetic multilayer structures consisting of thin ferromagnetic (F) layers and nonmagnetic spacers are known to exhibit plenty of phenomena, among which one can find those extensively studied for the last decades like anisotropic, giant and tunneling magnetoresistance or spin-transfer torque effect (STT),[1,2] and recently, current-driven spin−orbit torque (SOT) magnetization switching.[3]. Such layers combined with ferromagnetic ones (typically Co, CoFeB) are expected to have new spin transport properties related to the SOC, e.g., spin Hall effect (SHE) and Rashba−Edelstein effect (REE).[14,15] the SHE occurs in a single HM layer,[16] it is detectable in heterostructures with ferromagnets only, such as F/HM bi-17 and F/HM/F trilayers.[18,19] In these structures, the spin-polarized electrons can accumulate at the HM/F interfaces and may be efficiently injected into the F
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