Ultrathin Insertion Layers Research Articles

Enhancing Spin-Orbit Torque by Strong Interfacial Scattering From Ultrathin Insertion Layers

Increasing dampinglike spin-orbit torque (SOT) is both of fundamental importance for enabling new research into spintronics phenomena and also technologically urgent for advancing low-power spin-torque memory, logic, and oscillator devices. Here, we demonstrate that enhancing interfacial scattering by inserting ultra-thin layers within a spin Hall metals with intrinsic or side-jump mechanisms can significantly enhance the spin Hall ratio. The dampinglike SOT was enhanced by a factor of 2 via sub-monolayer Hf insertion, as evidenced by both harmonic response measurements and current-induced switching of in-plane magnetized magnetic memory devices with the record low critical switching current of ~73 uA (switching current density of 3.6x10^6 A/cm^2). This work demonstrates a very effective strategy for maximizing dampinglike SOT for low-power spin-torque devices.

Spin-orbit torque and spin pumping in YIG/Pt with interfacial insertion layers

We experimentally investigate spin-orbit torque and spin pumping in Y3Fe5O12 (YIG)/Pt bilayers with ultrathin insertion layers at the interface. An insertion layer of Cu suppresses both spin-orbit torque and spin pumping, whereas an insertion layer of Ni80Fe20 (permalloy, Py) enhances them in a quantitatively consistent manner with the reciprocity of the two spin transmission processes. However, we observe a large enhancement of Gilbert damping with the insertion of Py that cannot be accounted for solely by spin pumping, suggesting significant spin-memory loss due to the interfacial magnetic layer. Our findings indicate that the magnetization at the YIG-metal interface strongly influences the transmission and depolarization of pure spin current.

Effect of GaP and GaP/InGaP insertion layers on the structural and optical properties of InP quantum dots grown by metal-organic vapor phase epitaxy

A comparison of ultra-thin insertion layers (GaP and GaP/In0.4Ga0.6P) on InP self-assembled quantum dots (SAQDs) grown on GaAs (001) substrates using metal-organic vapor phase epitaxy (MOVPE) was studied. Atomic force microscopy (AFM) and photoluminescence (PL) were employed to characterize the optical and structural properties of the grown InP QDs. It is found that the QD dimension, size distribution and density strongly depend on the insertion layer thickness which led to tune the emission wavelength and narrowing of full width at half maximum (FWHM) at low temperature (20–250K) and at room-temperature PL measurements. This result is attributed to the improved QD size and quantum confinement effect arising from the insertion of the GaP and GaP/In0.4Ga0.6P layers.

Enhancement of exchange bias in thin PtMn antiferromagnets by Ru and Cr nano-lamination

In this work, we report a novel approach to facilitate the phase transformation, namely the introduction of ultrathin Ru and Cr nanolayers inside the PtMn layer. The concept is to bury one or more very thin (<1 monolayer) Ru or Cr layers in the PtMn at some distance from the interface. The effect of these insertion layers is to aid the FCC to FCT transformation by suppressing the constraining effect from the interface. Experimental results show an enhancement of the exchange bias field by adding these ultrathin insertion layers. The enhancement of the exchange bias field can be up to 10% compared to the structure without the insertion layer. From these results, it can be seen that significant exchange bias field enhancement can indeed be obtained with as little as 2Å of Ru insertion at 10Å from the interface. Similar results have been obtained with 1Å Cr insertion at the same PtMn layer position. These results illustrate the potential of nano-lamination of antiferromagnets as an avenue toward creation of novel spin valve and spintronic materials.