spin-state transition

An electronic transition from a high-spin state to a low-spin state, or vice versa. Example: With an increase in temperature Co³⁺ ions in LaCoO₃ transform from a low-spin state ( $t 2g 6 e g 0$ ) to the high-spin state ( $t 2g 4 e g 2$ ).

Source:

PAC, 1994, 66, 577 (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 591