Cooperative spin crossover: analog to digital – and back

Abstract

AbstractCooperativity among spin centres has long been the royal road to impose magnetic bistability in terms of thermal hysteresis. In this work we access magnetic multi-metastability of the iron(III) complex [Fe(L)2][BPh4] (1) at low temperature, in addition to thermal bistability. The packing of the low-spin and high-spin forms of crystalline1differs only marginally what ultimately leads to very minor thermal variation in the lattice constants. This indicates that the SCO-immanent breathing of the complex cation is almost fully compensated by the anion matrix. We believe that this structural conservatism is the origin of the unique cooling-rate dependence of the residual low-temperature magnetisation in1. The system state of1can be continuously tuned between the trapped high-spin (ON) and the relaxed low-spin state (OFF), as a simple function of the cooling rate. That is, cooperative spin crossover can be the source of bistable and multi-metastable system states in the very same material.