(color online) [(a) and (b)] V–I characteristics under different magnetic fields, with insets showing magnified parts of curves. [(c) and (d)] Curves of initial voltage versus magnetic field. [(e) and (f)] Calculated MR–B curves and S–B curves at I = 22 nA. Curves are obtained under [(a), (c), and (e)] 2-LEDs illumination and [(b), (d), and (f)] 4-LEDs illumination.