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.

DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights. • Users may download and print one copy of any publication from the public portal for the purpose of private study or research. • You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal. If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement:

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), surface anisotropy energy, and spin pumping at the Ir/Co interface are experimentally investigated by performing Brillouin light scattering. Contrary to previous reports, we suggest that the sign of the iDMI at the Ir/Co interface is the same as in the case of the Pt/Co interface. We also find that the magnitude of the iDMI energy density is relatively smaller than in the case of the Pt/Co interface, despite the large strong spin-orbit coupling (SOC) of Ir. The saturation magnetization and the perpendicular magnetic anisotropy (PMA) energy are significantly improved due to a strong SOC. Our findings suggest that an SOC in an Ir/Co system behaves in different ways for iDMI and PMA. Finally, we determine the spin pumping effect at the Ir/Co interface, and it increases the Gilbert damping constant from 0.012 to 0.024 for 1.5 nmthick Co. a)

A nonlinear magnetoresistance -called unidirectional spin-Hall magnetoresistance -is recently experimentally discovered in metallic bilayers consisting of a heavy metal and a ferromagnetic metal. To study the fundamental mechanism of the USMR, both ferromagnetic and heavy metallic layer thickness dependence of the USMR are presented in a Pt/Co/AlOx trilayer at room temperature. To avoid ambiguities, second harmonic Hall measurements are used for separating spin-Hall and thermal contributions to the non-linear magnetoresistance. The experimental results are fitted by using a drift-diffusion theory, with parameters extracted from an analysis of longitudinal resistivity of the Co layer within the framework of the FuchsSondheimer model. A good agreement with the theory is found, demonstrating that the USMR is governed by both the spin-Hall effect in the heavy metallic layer and the metallic diffusion process in the ferromagnetic layer.In the field of Spintronics, a new way of spin control based on the spin-Hall effect recently has attracted a great deal of attention. It originates from the spinorbit (SO) interaction which converts a charge current into a net flow of spin angular momentum, exerting a SO torque on the magnetization. This leads to an energy-efficient way of writing information to magnetic memories by switching a magnetic entity via sending a charge current through a nearby nonmagnetic metal 1,2 . Apart from writing, a possible way of reading the memory could be achieved by measuring a so-called spin-Hall magnetoresistance (SMR) 3,4 , i.e., a change in electrical resistance due to the spin Hall effect when the spin-accumulation is perpendicular or parallel to the magnetization. Although SMR provides a promising way towards reading memory devices using a twoterminal architecture, the fact that it can only distinguish between the perpendicular and parallel states limits its application.Very recently, a unidirectional contribution to magnetoresistance -called unidirectional spin-Hall magnetoresistance (USMR) -has been reported in a ferromagnetic/heavy metallic (FM/HM) bilayer structure 5-7 . Being different from the ordinary SMR, the resistance changes by reversing the magnetization or the current direction, which could be potentially utilized for reading operation. Based on a drift-diffusion-relaxation theory 8 , this nonlinear behavior is attributed to the dependence of electron mobility on spin-polarization, which is tuned by the spin-Hall effect induced spin accumulation. This spin accumulation is limited to a thin region at the FM/HM interface due to a finite spin diffusion length in both layers, leading to a non-trivial FM and HM thickness dependence of the USMR. So far, this a) E-mail: y.yin@tue.nl particular dependence on thickness is not evidenced by any experiments. Thus, a systematic investigation of how USMR depends on the layer thickness is urgently needed not only for a better understanding of the origin of USMR, but also for the enhancement of USMR in practical applications.In this paper, we...