Evidence of intrinsic ferromagnetism in individual dilute magnetic semiconducting nanostructures O-K. (a) Zn-L Zn-L 2,3

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1 SUPPLEMENTARY INFORMATION Evidence of intrinsic ferromagnetism in individual dilute magnetic semiconducting nanostructures O-K (a) O-K Fe-L Co-L 2,3 2,3 Zn-L Zn-L 2,3 2,3 (b) Intensity (a. u.) Figure S1. The channeling enhanced EEL spectra for (a) Co and (b) Fe doped ZnO at different orientation parameter ( Δ θ ). The spectra in both (a) and (b) are normalized using the O K-edge intensity. The arrow on the right side represents the direction of Δθ decreasing from ~ 1.8 to ~ -1.8mrad. The dependence of the normalized peak intensities (with respect to that of O-K edge) of Zn-L 2,3 edge, Co-L 2,3 edge, and Fe-L 2,3 edge on the orientation parameter ( Δ θ ) shown in Fig. 2. are plotted based on the corresponding channeling enhanced EEL spectra. nature nanotechnology 1

2 supplementary information Magnetization (μ B /Co 2+ ) T = 300 K Co-doped ZnO Magnetic field (koe) Figure S2. Magnetic hysteresis loops measured at 300 K. The inset shows the enlargement of the hysteresis loops near the origin. The Co-doped ZnO sample exhibits well-defined hysteresis loops at 300 K, which is indicative of robust high-t C ferromagnetic behavior. [X. F. Wang, J. B. Xu, B. Zhang, H. Yu, J. Wang, X. Zhang, J. Yu, Q. Li, Adv. Mater. 18, , 2006] Magnetization (emu/cm -3 ) T = 300 K Fe doped ZnO Magnetic field (KOe) Figure S3. Magnetization of the Fe-doped ZnO sample measured at 300K, showing paramagnetic behavior, i.e. no detectable hysteresis loop and the linear behavior lasting to very intense magnetic field suggest the absence of any ferromagnetic ordering. The relatively noisy signal is due to the sample measuring configuration a thin layer of Fe ion implanted ZnO nanoparticles residing on the Si substrate, which is diamagnetic. 2 2 nature nanotechnology

3 supplementary information Absorbance (a.u.) (a) ZnO 5.6 at.% Co/ZnO ZnO 5.6 at.% Co/ZnO Enlarged Intensity (a.u.) Emission from Co ion (b) Deep level defects emission ZnO 5.6 at.% Co/ZnO ZnO near band edge emission Figure S4 (a) Room temperature UV-visible absorption for the Co-doped ZnO nanocrystals and ZnO (as reference). The inset of the figure shows enlarged region between 1.7 and 2.3 ev. Absorption peaks at ca. 2.19, 2.02 and 1.86 ev (triple peak marked by vertical bars) are clear, which are assigned to the d-d* ligand-field transitions of the high-spin cobalt ion (3d 7 ; t 2g 5 e g 2 ) ions in tetrahedral crystal field surrounded by O 2 ions. The absorption peaks in the visible band is attributed to the 4 A 2 (F) 2 A 1 (G) and 4 A 2 (F) 4 T 1 (P) transitions, and that in the infrared is from the 4 A 2 (F) 2 E(G) transition [K. J. Kim, Y. R. Park, Appl. Phys. Lett. 81, 1420, 2001; P. Koidl, Phys. Rev. B 15, 2493, 1977], further corroborating the +2 valence state of Co and its taking the substitutional site of Zn in the ZnO lattice; and (b) Room temperature Cathodoluminescence (CL) spectra for the Co-doped ZnO nanocrystals and ZnO (as 3 nature nanotechnology 3

4 supplementary information reference). A sharp red band emission centered at ca ev is observed, which is due to the 4 T 1 (P) 4 A 2 (F) d-d* radiative transition of the internal Co ions in a tetrahedral crystal field [X. F. Wang, J. B. Xu, N. Ke, J. G. Yu, J. Wang, Q. Li, H. C. Ong, R. Zhang, Appl. Phys. Lett. 88, , 2006]. (a) Deep level defects emission Intensity (a.u.) Emission from Fe ion 4% Fe implanted ZnO As grown ZnO ZnO near band edge emission suppressed Intensity (a. u.) (b) Emission from Fe ion phonon sideband Figure S5: (a) CL of Fe implanted ZnO nanoparticles compared to as-grown and ZnO nanoparticles measured at 19 K. The spectra could be divided into three regions: ultra-violet (UV) luminescence (from ZnO band edge emission), luminescence of deep defect centres, and intra shell transitions of the Fe ions; (b) Enlarged cathodoluminescence spectrum of Fe implanted ZnO sample shows intra shell transitions of the Fe ion at 19 K. The transition at ev originates from the intra-shell recombination of Fe ion centres from the 4 T 1 (G) excited state to the 6 A 1 (S) ground state, suggesting its taking the substitutional site of Zn. The structured band on the low energy side of the direct intra-shell transition could be assigned to a phonon assisted side band. [S. Muller, M. J. Zhou, Q. Li, C. Ronning, Nanotechnology, 20, , 2009] 4 nature nanotechnology 4

5 supplementary information + - Figure S6. EMCD results and the corresponding difference spectra obtained under the Lorentz lens for Co-L 2,3 edges taken from the two chiral positions + and -, showing variation in the dichroism signals. Such variation could be due to the fact that EMCD results only represent the magnetization of the local region in the nanoparticles being probed, rather than a statistical summation of all particle contributions a situation associated with the macroscopic scale measurements. To illustrate the simplest case as an example, the magnetization from a pair of antiparallel magnetic domains could be canceled out in the macroscopic magnetic property measurement, resulting in very small (even zero) magnetic moment. As a comparison, both of them may give intense dichroism signals in the EMCD measurement, if the net moment in the probed area is aligned to a direction being either parallel or antiparallel to the incident electron beam (deviation from the parallel/antiparallel configuration would weaken the dichroism signals). As demagnetization occurs at low magnetic field, the orientations of individual domains will deviate from the external field direction at different degrees, and thus result in an intensity variation in the dichroism signals of the ZnCoO nanoparticles being probed. nature nanotechnology 5

6 supplementary information Figure S7. (a) Ray diagram of the convergent beam electron diffraction (CBED). 2α is the convergent angle of the incident electron beam, and g is the scattering vector of specific diffraction spot. Both the ALCHEMI-EELS and EMCD experiments were performed under the convergent beam and the corresponding EELS data were obtained in the diffraction mode. (b) The specimen was oriented in a two-beam condition when only the transmitted spot (0000) and a specific g hkil (hkil = 0002 in the present case) appeared in the diffraction pattern. In such a configuration, the angle between the incident electron beam and the hkil plane (θ) is the Bragg angle θ B. In the ALCHEMI-EELS measurement, deviation from the exact two beam condition (θ = θ B ) was created by the beam tilt, so that θ changed from θ < θ B to θ > θ B. An orientation parameter Δ θ (defined as Δ θ = θ θ B ) is used to describe such a deviation. The EELS data were then collected as a function of Δ θ. (c) In the EMCD measurement, while maintaining the exact two beam condition, a specific geometry in the diffraction pattern must be satisfied to observe the dichroic effect. The EMCD data was then collected in the + and position as indicated in the schematic (c). 6 nature nanotechnology