Domain Wall Dynamics in a Ferroelastic Spin Crossover Complex with Giant Magnetoelectric Coupling
Vibe B. Jakobsen, Elżbieta Trzop, Emiel Dobbelaar, Laurence C. Gavin, Shalinee Chikara, X. X. Ding, Minseong Lee, Kane Esien, Helge Müller‐Bunz, Solveig Felton, Éric Collet, Michael A. Carpenter, Vivien S. Zapf, Grace G. Morgan
Abstract
High Resolution Image Download MS PowerPoint Slide Pinned and mobile ferroelastic domain walls are detected in response to mechanical stress in a Mn 3+ complex with two-step thermal switching between the spin triplet and spin quintet forms. Single-crystal X-ray diffraction and resonant ultrasound spectroscopy on [Mn III (3,5-diCl-sal 2 (323))]BPh 4 reveal three distinct symmetry-breaking phase transitions in the polar space group series Cc → Pc → P 1 → P 1 (1/2) . The transition mechanisms involve coupling between structural and spin state order parameters, and the three transitions are Landau tricritical, first order, and first order, respectively. The two first-order phase transitions also show changes in magnetic properties and spin state ordering in the Jahn–Teller-active Mn 3+ complex. On the basis of the change in symmetry from that of the parent structure, Cc, the triclinic phases are also ferroelastic, which has been confirmed by resonant ultrasound spectroscopy. Measurements of magnetoelectric coupling revealed significant changes in electric polarization at both the Pc → P 1 and P 1 → P 1 (1/2) transitions, with opposite signs. All these phases are polar, while P 1 is also chiral. Remanent electric polarization was detected when applying a pulsed magnetic field of 60 T in the P 1→ P 1 (1/2) region of bistability at 90 K. Thus, we showcase here a rare example of multifunctionality in a spin crossover material where the strain and polarization tensors and structural and spin state order parameters are strongly coupled.