High-field magnetization and ESR in the triangular-lattice antiferromagnets Ba3MnSb2O9 and Ba3TNb2O9 (T=Ni, Co)

• In Ba3NiNb2O9, anisotropy is observed, exchange interactions are estimated.
• In Ba3MnSb2O9, single resonance peaksplits into double peaks below TN.
• Complicated ESR spectra have been observed in Ba3CoNb2O9 above TN.

We report high-field magnetization and electronic spin resonance (ESR) study on the triangular-lattice antiferromagnets Ba3MnSb2O9 and Ba3TNb2O9 (T=Ni, Co). The antiferromagnetic (AFM) ordering at TN is clearly characterized by the temperature dependent ESR spectra. In Ba3CoNb2O9, the complicated ESR peaks are observed above TN. No obvious frequency–field relationship could be deduced. In Ba3NiNb2O9, the AFM resonance with easy-plane anisotropy is observed, and accordingly, the magnetic exchange interactions are estimated. For Ba3MnSb2O9, the remarkable finding is that single resonance peak at paramagnetic state splits into double peaks below the ordering temperature. Possible interpretations for these unusual AFM resonance modes have been proposed.