Ferrotoroidic Ground State in a Heterometallic Cr$^{\mathrm{III}}$Dy$^{\mathrm{III}}_6$ Complex Displaying Slow Magnetic Relaxation

Toroidal quantum states are most promising for building quantum computing and information storage devices as they are insensitive to homogeneous magnetic fields, but interact with charge and spin currents, allowing this moment to be manipulated purely by electrical means. Coupling molecular toroids into larger toroidal moments via ferrotoroidic interactions can be pivotal not only to enhance ground state toroidicity, but also to develop materials displaying ferrotoroidic ordered phases, which sustain linear magneto-electric coupling and multiferroic behaviour. However, engineering ferrotoroidic coupling is known to be a challenging task. Here we have isolated a Cr$^{\mathrm{III}}$Dy$^{\mathrm{III}}_6$ complex, which exhibits the much sought-after ferrotoroidic ground state with an enhanced toroidal moment, solely arising from intramolecular dipolar interactions. Moreover, a theoretical analysis of the observed sub-Kelvin zero-field hysteretic spin dynamics of Cr$^{\mathrm{III}}$Dy$^{\mathrm{III}}_6$ reveals the pivotal role played by ferrotoroidic states in slowing down the magnetic relaxation, in spite of large calculated single-ion quantum tunnelling rates.