Field-free magnetization switching
is critical towards practical,
integrated spin-orbit torque (SOT)-driven magnetic random-access memory
with perpendicular magnetic anisotropy. Our work proposes a technique
to modulate the spin reflection and spin density of states within
a heavy-metal Pt through interfacing with a dielectric MgO layer.
We demonstrate tunability of the effective out-of-plane spin torque
acting on the ferromagnetic Co layer, enabling current-induced SOT
magnetization switching without the assistance of an external magnetic
field. The influence of the MgO layer thickness on effective SOT efficiency
shows saturation at 4 nm, while up to 80% of field-free magnetization
switching ratio is achieved with the MgO between 5 and 8 nm. We analyze
and attribute the complex interaction to spin reflection at the dielectric/heavy
metal interface and spin scattering within the dielectric medium due
to interfacial electric fields. Further, through substituting the
dielectric with Ti or Pt, we confirm that the MgO layer is indeed
responsible for the observed field-free magnetization switching mechanism.
Spin–orbit torque (SOT) induced magnetization switching and SOT modulation by interfacial coupling exhibit good potential in spintronic devices. In this work, we report the enhancement of damping-like field and SOT efficiency of up to 60% and 23%, respectively, in perpendicularly magnetized Pt/Co/HfOx heterostructures over a Pt/Co system at an optimal thickness of 2 nm HfOx. The SOT improvement is primarily attributed to the interfacial oxidization of the Co layer, and the strength is tunable via voltage-induced oxygen ion migration at the Co/HfOx interface. Our measurement reveals that by controlling gate voltages, the Co oxidation can be increased, which leads to the SOT efficiency enhancement. Our work promotes the SOT enhancement and modulation by oxidation effects for energy-efficient spintronic devices.
Spin–orbit torque (SOT) characterization techniques generally require the Hall cross that generally demands lithography resources and time. It is highly desirable to characterize SOT efficiencies with minimal sample processing time. Here, we demonstrate a lithography-free technique to determine the spin–orbit torque efficiency in a perpendicular magnetic anisotropy ferromagnetic heterostructure. By utilizing a customized four-point probe in a rhombus geometry, harmonic Hall measurement was performed on continuous films of a Pt/Co/Ti structure to characterize the spin–orbit torque efficiency. A correction factor, which is due to the non-uniform current distribution across the continuous film, was experimentally evaluated by taking the ratio of the measured damping-like field of the continuous film to that of a fabricated Hall device. Additionally, this correction factor is analytically derived and experimentally shown to be determined by the configuration of the probes and is independent of the structure material. Our measurement reveals that by performing a single calibration process for the particular set of probes, the same correction factor was validated on a second ferromagnetic heterostructure, Ti/Pt/Co/Ta; hence, it can be applied to other SOT films' stack measurements. Our four-probe harmonic Hall technique provides an alternative and swift way for SOT investigations by eliminating multiple lithography processes necessary in conventional approaches.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.