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

Abstract

The two-dimensional molecular conductor $\kappa$-(BETS)${}_2$Mn[N(CN)${}_2$]${}_3$ has been studied because of the intriguing magnetic coupling of the molecular $\pi$-electrons to the Mn${}^{2+}$ ions. Utilizing X-band electron spin resonance spectroscopy we have performed comprehensive investigations of the magnetic properties, in particular on the temperature and angular dependences of the spin susceptibility, the $g$-factor and the linewidth. Due to the $\pi$-$d$-coupling, a rearrangement of the $\pi$-spins occurs: At low temperatures 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. By carefully analyzing the angular dependence of $g(\theta )$ and $\Delta H(\theta )$ we reveal the influence of anisotropic Zeeman interaction in addition to spin-phonon coupling. We conclude the presence of two magnetically distinct BETS chains and discuss the possibility of altermagnetic order.

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