Magnetic decoupling in the triangular-lattice antiferromagnet Cu2(OH)3CHO2 studied by high-field magnetization and ESR

•The magnetic decoupling between the Cu1 ferromagnetic chain and the Cu2 antiferromagnetic chain has been revealed.•The high-field magnetization presents a metamagnetic transition at 1.7 T and a half-saturated ferromagnetic (FM)-like magnetization process.•The antiferromagnetic resonances of the antiferromagnetically coupled Cu1 FM chains were observed, showing the presence of significant magnetic anisotropy. The high-field magnetization and electron spin resonance (ESR) are reported for the two-dimensional triangular-lattice antiferromagnet Cu2(OH)3HCO2. The compound has an antiferromagnetic (AFM) order at TN = 4.9 K with the Curie-Weiss temperature θCW = − 3.8 K. The high-field magnetization up to 50 T exhibits a metamagnetic transition at 1.7 T followed by a half-saturated ferromagnetic (FM)-like magnetization process, showing the magnetic decoupling between the Cu1 FM chain and the Cu2 AFM chain. The unsaturated magnetization at 50 T serves as an evidence of much larger AFM exchange in the Cu2 chain. The temperature-dependent ESR spectra are in line with the development of magnetic correlations and AFM ordering. The observed ESR modes below TN originate from the AFM resonances of the antiferromagnetically coupled Cu1 FM chains. The zero-field gap of 111 GHz and the zero-frequency field of 2.4 T suggest the presence of significant magnetic anisotropy.