We review current challenges and perspectives in graphene spintronics, which is one of the most promising directions of innovation, given its room-temperature long-spin lifetimes and the ability of graphene to be easily interfaced with other classes of materials (ferromagnets, magnetic insulators, semiconductors, oxides, etc), allowing proximity effects to be harvested. The general context of spintronics is first discussed together with open issues and recent advances achieved by the Graphene Spintronics Work Package consortium within the Graphene Flagship project. Based on such progress, which establishes the state of the art, several novel opportunities for spin manipulation such as the generation of pure spin current (through spin Hall effect) and the control of magnetization through the spin torque phenomena appear on the horizon. Practical applications are within reach, but will require the demonstration of wafer-scale graphene device integration, and the realization of functional prototypes employed for determined applications such as magnetic sensors or nano-oscillators. This is a specially commissioned editorial from the Graphene Flagship Work Package on Spintronics. This editorial is part of the 2D Materials focus collection on 'Progress on the science and applications of twodimensional materials,' published in association with the Graphene Flagship. It provides an overview of key recent advances of the spintronics work package as well as the mid-term objectives of the consortium.

Frequency and power dependence of spin-current emission by spin pumping in a thin-film YIG/Pt system Castel, V.; Vlietstra, N.; van Wees, B. J.; Ben Youssef, J. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. This paper presents the frequency dependence of the spin-current emission by spin pumping in a hybrid ferrimagnetic insulator/normal metal system. The system is based on a ferrimagnetic insulating thin film of yttrium iron garnet (YIG, 200 nm) grown by liquid-phase epitaxy coupled with a normal metal with a strong spin-orbit coupling (Pt, 15 nm). The YIG layer presents an isotropic behavior of the magnetization in the plane, a small linewidth, and a roughness lower than 0.4 nm. Here we discuss how the voltage signal from the spin-current detector depends on the frequency (0.6-7 GHz), the microwave power, P in (1-70 mW), and the in-plane static magnetic field. A strong enhancement of the spin-current emission is observed at low frequencies, showing the appearance of nonlinear phenomena.

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The nonlocal transport of thermally generated magnons not only unveils the underlying mechanism of the spin Seebeck effect, but also allows for the extraction of the magnon relaxation length (λm) in a magnetic material, the average distance over which thermal magnons can propagate. In this study, we experimentally explore in yttrium iron garnet (YIG)/platinum systems much further ranges compared with previous investigations. We observe that the nonlocal SSE signals at long distances (d) clearly deviate from a typical exponential decay. Instead, they can be dominated by the nonlocal generation of magnon accumulation as a result of the temperature gradient present away from the heater, and decay geometrically as 1/d 2 . We emphasize the importance of looking only into the exponential regime (i.e., the intermediate distance regime) to extract λm. With this principle, we study λm as a function of temperature in two YIG films which are 2.7 and 50 µm in thickness, respectively. We find λm to be around 15 µm at room temperature and it increases to 40 µm at T = 3.5 K. Finite element modeling results agree with experimental studies qualitatively, showing also a geometrical decay beyond the exponential regime. Based on both experimental and modeling results we put forward a general guideline for extracting λm from the nonlocal spin Seebeck effect.

Graphene supported on a transition metal dichalcogenide substrate offers a novel platform to study the spin transport in graphene in presence of a substrate induced spin-orbit coupling, while preserving its intrinsic charge transport properties. We report the first non-local spin transport measurements in graphene completely supported on a 3.5 nm thick tungsten disulfide (WS 2 ) substrate, and encapsulated from the top with a 8 nm thick hexagonal boron nitride layer. For graphene, having mobility up to 16,000 cm 2 V −1 s −1 , we measure almost constant spin-signals both in electron and hole-doped regimes, independent of the conducting state of the underlying WS 2 substrate, which rules out the role of spin-absorption by WS 2 . The spin-relaxation time τ s for the electrons in graphene-on-WS 2 is drastically reduced down to ∼ 10 ps than τ s ∼ 800 ps in graphene-on-SiO 2 on the same chip. The strong suppression of τ s along with a detectable weak anti-localization signature in the quantum magneto-resistance measurements is a clear effect of the WS 2 induced spin-orbit coupling (SOC) in graphene. Via the top-gate voltage application in the encapsulated region, we modulate the electric field by 1 V/nm, changing τ s almost by a factor of four which suggests the electric-field control of the in-plane Rashba SOC. Further, via carrierdensity dependence of τ s we also identify the fingerprints of the D'yakonov-Perel' type mechanism in the hole-doped regime at the graphene-WS 2 interface.

What happens when a superconductor meets a normal conductor? This might seem a rather esoteric question, but it is the focus of much current research. It turns out that the superconductor can transfer some of its electronic properties to the normal conductor. This so-called superconducting proximity effect has been known about for several decades, but it is attracting renewed interest since the development of low-dimensional semiconductor structures. In particular, two-dimensional electron gases in which the electrons are confined to a 2-D plane, are now a standard tool for studying electron transport in two, one and even zero dimensions. Such systems are allowing researchers to probe the fundamental mechanisms that underlie the superconducting proximity effect.

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