Magnetism and magnetic anisotropy in Nb₃Cl₈ revealed by electron spin resonance

This study investigates the microscopic spin dynamics and anisotropic magnetic behavior in van der Waals kagome magnet Nb₃Cl₈ by employing electron spin resonance (ESR) spectroscopy on both powder and single-crystal samples over the temperature range of 5 K–300 K. The effective g, peak to peak linewidths (ΔH_pp), and double integrated intensities (I) were extracted from the ESR spectra to analyze the temperature-dependent evolution of spin–orbit coupling and spin–spin interactions. The formation of singlet ground state in single crystal Nb₃Cl₈ at T^*∼100 K is observed, evidenced by the maximum ΔH_pp and g at T^*, along with the decrease in intensity I, which is consistent to the reported non-magnetic transition in the single-crystal Nb₃Cl₈. Moreover, the spectral difference between H ∥ c and H ⊥ c configurations imply subtle magnetic anisotropy in single crystal Nb₃Cl₈. However, there is no non-magnetic transition was observed in powder Nb₃Cl₈ since the parameters of ΔH_pp and I keep stable at T^*. It might be attributed to the grain averaging and random orientation effects. Our study provides valuable insights into the magnetic interplay in Nb₃Cl₈ and prove the potential of ESR spectroscopy as a powerful tool for probing the intrinsic magnetism.