ESR Investigations of the Magnetic Anisotropy in $\kappa$-(BETS)$_2$Mn[N(CN)$_{2}$]$_3$

TL;DR

This study uses ESR spectroscopy to explore magnetic anisotropy and spin behavior in a two-dimensional molecular conductor, revealing temperature-dependent spin rearrangements, anisotropic Zeeman effects, and potential altermagnetic order.

Contribution

It provides the first detailed ESR analysis of magnetic anisotropy and spin dynamics in $$-(BETS)$_2$Mn[N(CN)$_2$]$_3$, highlighting $$-$d$ coupling effects and magnetic chain distinctions.

Findings

Enormous in-plane $g$-factor shifts at low temperatures

Significant linewidth broadening and susceptibility increase upon cooling

Evidence of two magnetically distinct BETS chains and possible altermagnetic order

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.