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1 Engineered materials for all-optical helicity-dependent magnetic switching S. Mangin 1,2, M. Gottwald 1, C-H. Lambert 1,2, D. Steil 3, V. Uhlíř 1, L. Pang 4, M. Hehn 2, S. Alebrand 3, M. Cinchetti 3, G. Malinowski 2,5, Y. Fainman 4, M. Aeschlimann 3, and E.E. Fullerton 1,4 1) Center for Magnetic Recording Research, University of California San Diego, La Jolla, CA , USA 2) Institut Jean Lamour, UMR CNRS 7198 Université de Lorraine- boulevard des aiguillettes, BP 70239, F Vandoeuvre cedex, France 3) Department of Physics and Research Center OPTIMAS University of Kaiserslautern, Erwin Schroedinger Str. 46, D Kaiserslautern, Germany 4) Department of Electrical and Computer Engineering, University of California San Diego, La Jolla, CA , USA 5) Laboratoire de Physique des Solides, Université Paris-Sud, CNRS UMR 8502, Orsay, France Supplementary Information that includes additional Figures that compliment that data shown in the main text. Figure S1: Example of the optical response exhibiting a mixed behavior between thermal demagnetization shown in Fig. 2a and AO-HDS shown in Fig. 2b. For [Co(0.8nm)/Tb(0.5nm)]x19 multilayers two types of polarized laser beam were swept over the sample and the magnetization pattern was imaged: from top to bottom right circularly polarized light ( +), left circularly polarized light ( -). In the image dark contrast corresponds to one orientation of magnetization and light contrast the opposite. There is domain formation but the nature of the domains is dependent on the light helicity. NATURE MATERIALS 1

2 Figure S2: Evolution of the coercive field (HC ) as a function of the RE concentration (x) for 25-nm alloy films of (a) GdxFeCo1-x, (b) TbxCo1-x, and x (c) HoxFeCo1-x and (d)dyxco1-x. The red dots show concentration for which thermal demagnetization is observed, whereas the green stars are for AO-HDS. 2 NATURE MATERIALS

3 SUPPLEMENTARY INFORMATION Figure S3: X-ray reflectivity curves for Tb/Co multilayers showing clear super-structure peaks (red arrows) that confirm the distinct layers and periodic nature of the multilayer samples NATURE MATERIALS 3

4 Figure S4: Evolution of the coercive fields (HC) as a function of (a) the Tb concentration (x) in [Tb/ Co] multilayers and (b) the Ho concentration in [Ho/ CoFe] multilayers. The red dots show concentration for which thermal demagnetization has been observed whereas the green stars are for AO-HDS. For the Tb/Co multilayers the measurement was limited to 20 koe so measurements for samples HC>20 koe are only a lower limit. Figure S5: Evolution of the coercive fields (HC ) as a function of the number N for function N for (a) [Tb(0.5nm)/Co(0.45nm)]N,/[Tb(035nm)/Co(0.7nm)]25-N and (b) [Tb(0.5nm)/Co(0.45nm)] N,/[Tb(0.35nm)/Co(0.53nm)] 25-N exchange coupled multilayers. The red dots show concentrations for which Thermal demagnetization has been observed, whereas the green stars are for AO-HDS. 4 NATURE MATERIALS

5 SUPPLEMENTARY INFORMATION 0.08 m (memu) H (koe) Figure S6: Magnetization as a function of the applied magnetic field perpendicular to the film plane for a [Co(1nm)/Ir(0.4nm)/Co(0.4nm)/Ni(0.6nm)/Pt(0.3nm)/Co(0.4nm)/Ir(0.4nm)]x5 multilayer. The sample includes a Ta(4nm)/Pd(3nm) seed and Pd(3 nm capping) layers. This measurements show that an applied magnetic field of about 100 koe is needed to overcome the antiferromagnetic exchange coupling between the Co(1nm) and the Co(0.4nm)/Ni(0.6nm)/Pt(0.3nm)/Co(0.4nm) layers H C (koe) M (emu/cm 3 ) 6 M H C T (K) Figure S7: Measurements of the remanent magnetization M and coercive field HC on a [Co(1nm)/Ir(0.4nm)/Co(0.4nm)/Ni(0.6nm)/Pt(0.6nm)/Co(0.4nm)/Ir(0.4nm)]x5/. The temperature dependence of M and HC allows us to define a compensation temperature TMcomp= 300 K. 0 NATURE MATERIALS 5

6 Figure S8: Schematic of magnetic measurements apparatus showing a 50fs laser exiting the sample and the domain structure imaged using a Faraday microscope. Power Threshold ( W) TD AO-HDS % Tb Figure S9: Threshold power for either achieving TD or AO-HDS in Tb/Co multilayer samples as a function of Tb concentration. 6 NATURE MATERIALS