Direct Observation of Interfacial Dzyaloshinskii-Moriya Interaction from Asymmetric Spin-wave Propagation in W/CoFeB/SiO2 Heterostructures Down to Sub-nanometer CoFeB Thickness

Abstract

Interfacial Dzyaloshinskii-Moriya interaction (IDMI) is important for its roles in stabilizing the skyrmionic lattice as well as soliton-like domain wall motion leading towards new generation spintronic devices. However, achievement and detection of IDMI is often hindered by various spurious effects. Here, we demonstrate the occurrence of IDMI originating primarily from W/CoFeB interface in technologically important W/CoFeB/SiO2 heterostructures using Brillouin light scattering technique. Due to the presence of IDMI, we observe asymmetry in the peak frequency and linewidth of the spin-wave spectra in the Damon-Eshbach (DE) geometry at finite k wave-vectors. The DMI constant is found to scale as the inverse of CoFeB thickness, over the whole studied thickness range, confirming the presence of IDMI in our system without any extrinsic effects. Importantly, the W/CoFeB interface shows no degradation down to sub-nanometer CoFeB thickness, which would be useful for devices that aim to use pronounced interface effects.

Spin Waves in Thin Films and Magnonic Crystals with Dzyaloshinskii–Moriya Interactions

“…The first observation of nonreciprocal spin waves [16,68,69] caused by interfacial DMI was achieved by Zakeri et al [70,71] using the spin-polarized electron energy loss (SPEEL) experimental technique. A few years later, nonreciprocal spin waves were observed by means of BLS spectroscopy in several ferromagnet/heavy metal interfaces [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87]. In agreement with the results of Zakeri et al [70,71], these numerous experiments have shown that interfacial DMI creates a noticeable frequency asymmetry in the spin-wave dispersion of counterpropagating Damon-Eshbach (DE) spin waves.…”

“…In particular, this numerical technique can be used to calculate the spectrum of spin waves, and when a DMI is present, it reveals different properties characteristic of these systems, such as the spin-wave asymmetry. In this context, simulations have successfully supported theoretical formulations [80,96,97,99,[132][133][134][135][136][137] and experimental measurements [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87]138] on thin-film systems with a homogeneous DMI. A micromagnetic simulation is based on numerically discretizing the continuum description of the magnetic system into a mesh of magnetic moments whose arrangement depends on the discretization method.…”

“…Then, by measuring f , the strength of the interfacial DMI can be directly measured, as was theoretically proposed in Ref. [96], and then measured by several groups, mainly using BLS [72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87], as summarized in Tables 5.2 and 5.3. It is worth to mention that the estimation of the DMI strength through measurement of the frequency difference between counterpropagating spin waves, in the field-polarized case, should be the most reliable method, since there are no assumptions about the possible magnetic texture.…”

All-optical detection of the spin Hall angle inW/CoFeB/SiO2heterostructures with varying thickness of the tungsten layer

“…3(d the film stacks investigated in this study, M eff is found to be close to the saturation magnetization M s obtained using vibrating sample magnetometer. From this we infer that interface anisotropy is negligibly small in these heterostructures [31]. Fig.…”

Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Film Heterostructures

“…Brillouin Light Scattering (BLS) spectra were recorded using a Sandercock-type (3 + 3) pass tandem Fabry-Pérot interferometer and a p -polarized (wavelength of 532 nm with 300 mW power) single longitudinal mode solid state laser. The details of the BLS set up can be found elsewhere 75 . The spectra were recorded in the conventional backscattering geometry at various wave vector orientations selected by mounting the sample on the angle-controlled sample holder providing a range of 10°−60° incident angles corresponding to wave vectors k x lying in the range of 0.004–0.0204 nm −1 .…”