Angular dependence of spin-flop transition in triangular lattice antiferromagnet Cu 2 (OH) 3 Br.

We report angular dependence of spin-flop transition in triangular lattice antiferromagnet Cu 2 (OH) 3 Br by angle-dependent magnetization and ESR measurements. The results show that the antiferromagnetic easy magnetization axis is the diagonal direction ( θ = 45°) of the ac * plane, i.e., the orientation of Cu1 spins based on the magnetic structure (2020 Phys. Rev. Lett. 125 037204), whereas the spin-flop axis is the b axis. A phenomenological model is proposed to describe the angle-dependent spin-flop transitions. Based on this model, Cu1 spins are sensitive to external magnetic field, while Cu2 spins are robust against to the field, showing partial decoupling. The model is expected to be used in other uniaxial antiferromagnets with a more general easy axis and complex spin-flop transitions.