Electronic properties of the dimerized organic conductor $\kappa$-(BETS)${}_2$Mn[N(CN)${}_2$]${}_3$

Abstract

The two-dimensional molecular conductor $\kappa$-(BETS)${}_2$Mn[N(CN)${}_2$]${}_3$ undergoes a sharp metal-to-insulator phase transition at $T_{\mathrm{MI}}\approx$ 21 K, which has been under scrutiny for many years. We have performed comprehensive infrared investigations along the three crystallographic directions as a function of temperature down to 10 K, complemented by electron spin resonance and dc-transport studies. The in-plane anisotropy of the optical conductivity is more pronounced than in any other $\kappa$-type BEDT-TTF or related compounds. The metal-insulator transitions affects the molecular vibrations due to the coupling to the electronic system; in addition we observe a clear splitting of the charge-sensitive vibrational modes below $T_{\mathrm{MI}}$ that evidences the presence of two distinct BETS dimers in this compound. The Mn[N(CN)${}_2$]${}_3^{-}$ layers are determined by the chain structure of the anions resulting in a rather anisotropic behavior and remarkable temperature dependence of the vibronic features. At low temperatures the ESR properties are affected by the Mn${}^{2+}$ ions via $\pi$-$d$-coupling and antiferromagnetic ordering within the $\pi$-spins: The $g$-factor shifts enormously with a pronounced in-plane anisotropy that flips as the temperature decreases; the lines broaden significantly; and the spin susceptibility increases upon cooling with a kink at the phase transition.

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Cited by in corpus (1)

• ESR Investigations of the Magnetic Anisotropy in $\kappa$-(BETS)${}_2$Mn[N(CN)${}_2$]${}_3$