Cooperative Jahn-Teller Distortion, Phase Transitions, and Weak Ferromagnetism in the KCrF₃ Perovskite

At ambient conditions, the ternary fluoride with formula KCrF3 adopts a perovskite-type structure and incorporates the Jahn-Teller active Cr2+ (d4) whose electronic configuration and magnetic response are analogous to those of Mn3+ (d4) and Cu2+ (d9). These ingredients make it an attractive system to study owing to the striking similarities with LaMnO3 and the expected strong interplay between spin, orbital, and structural ordering phenomena. Indeed, probing the properties of KCrF3 as a function of temperature (5 < T < 300 K) has revealed a structurally and magnetically far richer phase diagram than hitherto supposed. We found that KCrF3 exhibits large cooperative Jahn-Teller distortions which are driven by orbital ordering, a series of temperature induced complex structural transitions, and weak ferromagnetism which is reminiscent of what is observed in LaMnO3.