Domain Wall Dynamics in a Ferroelastic Spin Crossover Complex with Giant Magnetoelectric Coupling.
J Am Chem Soc 2021;
144:195-211. [PMID:
34939802 PMCID:
PMC8759087 DOI:
10.1021/jacs.1c08214]
[Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022]
Abstract
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Pinned and mobile
ferroelastic domain walls are detected in response
to mechanical stress in a Mn3+ complex with two-step thermal
switching between the spin triplet and spin quintet forms. Single-crystal
X-ray diffraction and resonant ultrasound spectroscopy on [MnIII(3,5-diCl-sal2(323))]BPh4 reveal three
distinct symmetry-breaking phase transitions in the polar space group
series Cc → Pc → P1 → P1(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 Mn3+ 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 → P1 and P1 → P1(1/2) transitions, with opposite signs. All these phases are polar, while P1 is also chiral. Remanent electric polarization was detected
when applying a pulsed magnetic field of 60 T in the P1→ P1(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.
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