Fig. 1. (Color online) Schematic diagram for including oxygen in crystalline and amorphous metals. FM denotes ferromagnetic metals.

Fig. 2. (Color online) (a) Schematic diagram for depositing Co–Fe–Ta–B–O thin films. (b)–(j) oxidation process.

Fig. 3. (Color online) High-resolution transmission electron microscopy (HRTEM) images of the CFTBO_xsystem (a) CFTB, (b) CFTBO₄₄, and (c) CFTBO₄₆.

Fig. 4. (Color online) (a) Optical transmittance of the CFTBO_x system. (b) Optical bandgap and (c) photoluminescence spectrum of the CFTBO₄₆ thin film.

Fig. 5. (Color online) The normalized resistivity ρ/ρ₀ as a function of temperature (ρ₀ is the room temperature resistivity) for the CFTBO_x (16≤ x ≤ 46 at%) thin films. Inset is the plot of ln(ρ/ρ₀) versus 1/T^1/2 based on the experimental data of the CFTBO₄₆ thin film.

Fig. 6. (Color online) Magnetic behavior of the CFTBO_x (16 ≤ x ≤ 46 at%): (a) Magnetic field dependence of the magnetization (M–H) curves measured at room temperature. (b) Saturation magnetization (M_s) variation with the oxygen contents. (c) Zero-field-cooling (ZFC) and field-cooling (FC) curves measured at an external field of 100 Oe. (d) High-temperature magnetization–temperature (M–T) curve measured for the CFTBO₄₆ thin film at an external field of 100 Oe.

Fig. 7. (Color online) Schematic diagrams for fabricating p–n (b) and p–n–p heterojunctions based on the CFTBO₄₆ thin film and n-type Si. The Si is heavily doped with phosphorous and has resistivity of order of 10^–3 Ω·cm. (c) The I–V curves for the heterojunctions of (a) and (b). The figure was adopted from Ref. [26].

Fig. 8. The threshold voltage (V_th) of the p–n heterojunctions increasing with decreasing the resistivity (ρ) of the n-type Si.

Fig. 9. (Color online) Electric-field control of the ferromagnetism in the CFTBO₄₆ AMS. (a) Schematic diagram of the experimental set-up for applying gate voltages (V_G) on the thin films through a drop of ionic liquid. The thickness of an insulating HfO₂ layer is about 2 nm. (b) Variation of M–H curves with different V_G measured at 300 K.

Fig. 10. (Color online) (a) HRTEM image of the newly developed CFTBO AMS. (b) Schematic diagrams for the electric-field control of carrier concentrations at different V_G. (c) M_s increaisng with both positive and negative V_G.