In magnetic multilayer systems, a large spin-orbit coupling at the interface between heavy metals and ferromagnets can lead to intriguing phenomena such as the perpendicular magnetic anisotropy, the spin Hall effect, the Rashba effect, and especially the interfacial Dzyaloshinskii–Moriya (IDM) interaction. This interfacial nature of the IDM interaction has been recently revisited because of its scientific and technological potential. Here we demonstrate an experimental technique to straightforwardly observe the IDM interaction, namely Brillouin light scattering. The non-reciprocal spin wave dispersions, systematically measured by Brillouin light scattering, allow not only the determination of the IDM energy densities beyond the regime of perpendicular magnetization but also the revelation of the inverse proportionality with the thickness of the magnetic layer, which is a clear signature of the interfacial nature. Altogether, our experimental and theoretical approaches involving double time Green's function methods open up possibilities for exploring magnetic hybrid structures for engineering the IDM interaction.

The interfacial Dzyaloshinskii-Moriya interaction (DMI) is intimately related to the prospect of superior domain-wall dynamics and the formation of magnetic skyrmions. Although some experimental efforts have been recently proposed to quantify these interactions and the underlying physics, it is still far from trivial to address the interfacial DMI. Inspired by the reported tilt of the magnetization of the side edge of a thin film structure, we here present a quasi-static, straightforward measurement tool. By using laterally asymmetric triangular-shaped microstructures, it is demonstrated that interfacial DMI combined with an in-plane magnetic field yields a unique and significant shift in magnetic hysteresis. By systematic variation of the shape of the triangular objects combined with a droplet model for domain nucleation, a robust value for the strength and sign of interfacial DMI is obtained. This method gives immediate and quantitative access to DMI, enabling a much faster exploration of new DMI systems for future nanotechnology.

The interfacial Dzyaloshinskii–Moriya interaction (iDMI) and the interfacial perpendicular magnetic anisotropy (iPMA) between a heavy metal and ferromagnet are investigated by employing Brillouin light scattering. With increasing thickness of the heavy-metal (Pt) layer, the iDMI and iPMA energy densities are rapidly enhanced and they saturate for a Pt thickness of 2.4 nm. Since these two individual magnetic properties show the same Pt thickness dependence, this is evidence that the iDMI and iPMA at the interface between the heavy metal and ferromagnet, the physical origin of these phenomena, are effectively enhanced upon increasing the thickness of the heavy-metal layer.

The Rashba effect leads to a chiral precession of the spins of moving electrons while the Dzyaloshinskii-Moriya interaction (DMI) generates preference towards a chiral profile of local spins. We predict that the exchange interaction between these two spin systems results in a 'chiral' magnetoresistance depending on the chirality of the local spin texture. We observe this magnetoresistance by measuring the domain wall (DW) resistance in a uniquely designed Pt/Co/Pt zigzag wire, and by changing the chirality of the DW with applying an in-plane magnetic field. A chirality-dependent DW resistance is found, and a quantitative analysis shows a good agreement with a theory based on the Rashba model. Moreover, the DW resistance measurement allows us to independently determine the strength of the Rashba effect and the DMI simultaneously, and the result implies a possible correlation between the Rashba effect, the DMI, and the symmetric Heisenberg exchange.In a magnetic system with inversion symmetry breaking combined with spin-orbit coupling (SOC), a variety of chirality-related phenomena occur. For instance, due to the Rashba effect [1], the spins of the conduction electrons flowing at an interface are subject to an effective in-plane magnetic field due to the relativistic SOC, resulting in spin precession around the field during its transport. In this case, the direction of the magnetic field depends on the electron flow direction. In contrast, the precession of the conduction spins, as can be seen from comparing Figs. 1(a) and 1(b), is independent of the flow direction and shares the same rotational sense (denoted by a chirality of electrons, C e ) [2]. Apart from the chiral behavior of the conduction spins, the chiral nature of localized spins has recently been discovered in ferromagnetic materials with inversion asymmetry and SOC. This gives rise to the Dzyaloshinskii-Moriya interaction (DMI) [3,4] leading to a chiral spin texture of the localized spins (C m ), manifested as Néel type magnetic domain walls (DWs) [5] and magnetic skyrmions [6], which are crucial to the future design of spintronic devices.Although these two effects originate in different spin systems, one can speculate about their interplay through exchange interaction between the conduction and localized spins [7][8][9]. This results in a magnetoresistance (MR) which arises when the conduction electron spins propagate with a fixed chirality due to Rashba-type SOC and interact with the chiral DMI-induced magnetic texture. As shown in Figs. 1(c) and 1(d), this should lead to lower (higher) resistance when C e is identical (opposite) to C m . This MR can be termed as 'chiral MR', since the magnitude of the MR varies for spin The chirality of the profile of the spin precession is identical (Ce = +1) for both signs of k. (c)(d) Inside a chiral magnetic texture with chirality Cm (green arrows), the rotation of electron spins generally follow the local spins due to exchange interaction while finite degree of misalignment is inevitable, which gives rise to t...

We investigate the sign of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) energy density in system with inversion symmetry breaking for amorphous and polycrystalline ferromagnetic layers (CoFeB, Co) sandwiched by two different or the same heavy metals (Pt, Ta). By employing Brillouin light scattering, we observe non-reciprocal spin-wave dispersions which is a fingerprint of iDMI in SiO 2 /(Pt,Ta)/(CoFeB, Co)/(Pt,Ta) systems. We carefully confirm that the signs of DMI of structurally inverted systems are changed accordingly. Negative iDMI for SiO 2 /Pt/(CoFeB, Co)/Ta and positive iDMI for SiO 2 /Ta/ (CoFeB, Co)/Pt are observed, and iDMI of the symmetric structures (Pt/CoFeB/Pt and Ta/ CoFeB/Ta) are not measureable with our Brillouin light scattering setup due to a negligible iDMI. For amorphous CoFeB, the magnitudes of iDMI are the same within the experimental error regardless the stacking order. For the textured Co, however, the magnitude of iDMI for Pt/Co/Ta is about 30 % larger than Ta/Co/Pt structure.