100 50 0 -15 -10 -5 0 Intensity (arb. units) 800 795 790 785 780 775 Photon Energy (eV) -1 0 Normalized Intensity 782 780 778 776 1.0 0.8 0.6 0.4 0.2 0 Magnetization ( GLYPH<s109> B /Co) 7 6 5 4 3 2 1 0 Magnetic Field (T) Zn$_{0.9}$Co$_{0.1}$O P$_{O2}$ =10$^{-3}$ Pa 4.5 T 7.0 T T  = 20 K Co 2 p  XAS XMCD Co 2 p$_{3/2}$ x =0.07,  P$_{O2}$ =10$^{-4}$ Pa, x =0.10,  P$_{O2}$ =10$^{-2}$ Pa, x =0.10,  P$_{O2}$ =10$^{-3}$ Pa, x =0.10,  P$_{O2}$ =10$^{-4}$ Pa (a) (b) Fit function: CH /( T – GLYPH<s113> ) +  M$_{s}$ T  = 20 K  Fitted FIG. 3: (Color online) Magnetic-field dependence of the XMCD spectra of Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O thin films. (a) XMCD spectra of the x = 0 . 10, P$_{O2}$ = 10 − 3 sample at T = 20 K and at various magnetic fields. The inset shows the XMCD spectra normalized to the negative peak height at hν = 778 . 5 eV. (b) H dependence of the total magnetization ( M$_{tot}$ ) estimated using the XMCD sum rules at T = 20 K. Solid curves are the results of fitting to the Curie-Weiss law, CH/ ( T − θ ) + M$_{s}$ . 18