Fig. 3. (a) χ _M T and HS fraction versus temperature for 1^Pt (blue: cooling, red: heating) displaying the complete four-step SCO behaviour. Step regions and nHS/HS^total for the respective five distinct spin states are indicated. (b) χ _M T versus temperature for 1^Pd (black (○): thermal spin transition, red (Δ): irradiation at 10 K with λ = 510 nm and green (□): relaxation in the dark showing photo-excitation properties). Inset: reversibility of photo-induced state using alternating 510 nm (‘on’) and 830 nm (‘off’) wavelengths.