Ferromagnetism out of charge fluctuation of strongly correlated electrons in $\kappa$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$Br

Abstract

We perform magnetic susceptibility and magnetic torque measurements on the organic $\kappa$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$Br, which is recently suggested to host an exotic quantum dipole-liquid in its low-temperature insulating phase. Below the metal-insulator transition temperature, the magnetic susceptibility follows a Curie-Weiss law with a positive Curie-Weiss temperature, and a particular $M\propto \sqrt{H}$ curve is observed. The emergent ferromagnetically interacting spins amount to about 1/6 of the full spin moment of localized charges. Taking account of the possible inhomogeneous quasi-charge-order that forms a dipole-liquid, we construct a model of antiferromagnetically interacting spin chains in two adjacent charge-ordered domains, which are coupled via fluctuating charges on a Mott-dimer at the boundary. We find that the charge fluctuations can draw a weak ferromagnetic moment out of the spin singlet domains.

arXiv comment9 pages, 5 figures, Supplementary Material attached

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• Anomalously field-susceptible spin soft-matter emerging in an electric-dipole liquid candidate
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• Charge and spin interplay in a molecular-dimer-based organic Mott insulator
• Tuning Charge Order in $\kappa$-(BEDT-TTF)${}_2$Hg(SCN)${}_2$X (X=Br, Cl) via Uniaxial Strain
• ${}^{13}$C NMR observation of a nonmagnetic charge-ordered state in the organic conductor $\kappa$-(ET)${}_2$Hg(SCN)${}_2$Cl