ESR investigations of the magnetic anisotropy in κ − ( BETS ) 2 Mn [ N ( CN ) 2 ] 3

The two-dimensional molecular conductor κ − ( BETS ) 2 Mn [ N ( CN ) 2 ] 3 has been studied because of the intriguing magnetic coupling of the molecular π electrons to the Mn 2 + ions. Utilizing -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 π − d coupling, a rearrangement of the π 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 ( θ ) and Δ H ( θ ) 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.