Extraction of Dzyaloshinskii-Moriya interaction from propagating spin waves

Abstract

The interfacial Dzyaloshinskii-Moriya interaction (iDMI) is of great interest in thin-film magnetism because of its ability to stabilize chiral spin textures. It can be quantified by investigating the frequency non-reciprocity of oppositely propagating spin waves. However, as the iDMI is an interface interaction the relative effect reduces when the films become thicker making quantification more difficult. Here, we utilize all-electrical Propagating Spin Wave Spectroscopy (PSWS) to disentangle multiple contributions to spin wave frequency non-reciprocity to determine the iDMI. This is done by investigating non-reciprocities across a wide range of magnetic layer thicknesses (from 4 to 26 nm) in Pt/Co/Ir, Pt/Co/Pt, and Ir/Co/Pt stacks. We find the expected sign change in the iDMI when inverting the stack order, and a negligible iDMI for the symmetric Pt/Co/Pt.We additionally extract a difference in surface anisotropies and find a large contribution due to the formation of different crystalline phases of the Co, which is corroborated using nuclear magnetic resonance and high-resolution transmission-electron-microscopy measurements. These insights will open up new avenues to investigate, quantify and disentangle the fundamental mechanisms governing the iDMI, and pave a way towards engineered large spin-wave non-reciprocities for magnonic applications.

A Zero-field Nuclear Magnetic Resonance Spectroscopy Study on the Structure Property Relationship in Co thin Films

“…As explained in the previous section, we need five Gaussian lines to fit spectra of both the 10 nm and the 25 nm film with the resonance with the lowest frequency (red Gaussian line in panels (a),(b) of We cannot locate the exact position of the different phases within the Co stacks because ZF NMR is an integral method. But the qualitative TEM study conducted in the work of Lucassen et al supports our model [10] and allows to locate the respective environments within the film stacks. Therefore we can safely assume that we will find the f cc phase at the bottom of the Co stack because of the lattice strain introduced by the Pt (111) layer.…”

“…Part of the study, namely the ZF NMR frequency spectra and its superficial interpretation, was already published in the supplemental of Lucassen et al [10]. In this work, we go beyond the previous study and present in detail the phase and defect composition in two Co film stacks with different thickness.…”

“…Recently, Lucassen et al examined the iDMI in Co film stacks with varying thicknesses (4 to 26 nm) utilizing propagating spin-wave spectroscopy (PSWS) [10]. It turned out that for investigating the nonreciprocity as a function of Co layer thickness for Pt/Co/Ir, Pt/Co/Pt and Ir/Co/Pt systems, a careful disentanglement of contributions other than the iDMI to the nonreciprocity is vital.…”

Chiral Spin-Wave Velocities Induced by All-Garnet Interfacial Dzyaloshinskii-Moriya Interaction in Ultrathin Yttrium Iron Garnet Films

“…However, independent evidence for the DMI was not provided. Spin waves provide a prevailing methodology [22][23][24][25][26][27][28] for probing the DMI in metallic multilayers. DMI is the fundamental mechanism to form chiral spin textures, such as skyrmions [29][30][31].…”

“…DMI is the fundamental mechanism to form chiral spin textures, such as skyrmions [29][30][31]. Most previous studies on the interfacial DMI focus on measuring frequency shifts δf between counter-propagating spin waves (with wavevectors +k and −k) using Brillouin light scattering (BLS) [25,27] or all-electrical spin-wave spectroscopy (AESWS) [26,28]. It has been theoretically predicted that the interfacial DMI can generate not only a frequency shift, but also asymmetric spin-wave group velocities [24].…”