RESULTS AND DISCUSSION polarized x rays were obtained by reversing photon helicity at each photon energy in the total-electron-yield mode. The µ + and µ − spectra were averaged between spectra for the positive and negative applied magnetic fields so as to eliminate spurious signals. The degree of circular polarization of x-rays was over 90 %. External magnetic fields were applied perpendicular to the sample surface. Circularly-polarized x-ray absorption spectra under each experimental conditions have been normalized to the maximum height of the Co 2 p XAS [( µ + + µ $^{−}$) / 2] spectrum. Backgrounds of the XAS spectra at the Co 2 p edge were assumed to be hyperbolic tangent functions. Annealing of the P$_{O2}$ =10 − 2 Pa sample was performed at 700 $^{◦}$C and ∼ 10 − 7 Pa for 5 min. For surface cleaning, Ar + ion sputtering and subsequent 250 $^{◦}$C annealing (well below the deposition temperatures) were performed in a high vacuum of 10 − 7 Pa. Figure 1 shows the magnetic-field ( H ) and temperature ( T ) dependences of the mag- netization ( M ) measured using a SQUID magnetometer. Although the raw magnetization data decreases with H due to the diamagnetic contribution from the substrate as shown in the inset of Fig. 1(a), there are small but finite ferromagnetic signals. By subtracting the linear component at high magnetic fields from the raw data, the ferromagnetic hysteresis loops have been extracted at 10 and 300 K, as shown in the main panel of Fig. 1(a). The hysteresis loop at 300 K implies that T$_{C}$ of the ferromagneitc component is above room temperature. Here, the coercive fields are found to be 100-200 Oe. The M$_{s}$ of the films was of the order of 10 − 2 µ$_{B}$ /Co, indicating that less than 1 % of the Co ions participate in the ferromagnetism if the Co ions is in the high spin Co 2+ state. The M$_{s}$ slightly decreases with increasing temperature. The M$_{s}$ ’s of the present homo-epitaxial films are as small as 5 − 10 % of that of the previous hetero-epitaxial one because of the high P$_{O2}$ , although the present Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O thin film has higher crystal quality than the previous one. Assuming that the diamagnetic and ferromagnetic responses hardly change with temperature, the paramagnetic susceptibilities have been obtained by subtracting the slopes of the M - H curves taken at different T ’s, as shown in Fig. 1(b). One can see that the paramagnetic signals increase with decreasing T in the low T region. The observations thus suggest the presence of both the paramagnetic and ferromagnetic components in the present Zn$_{1}$$_{−}$$_{x}$Co$_{x}$O thin films. 6