Spin-flop transition in the easy-plane antiferromagnet nickel oxide

NiO is a room-temperature antiferromagnetic (AF) insulator with important applications in AF spintronics. Although it is considered a prototypical AF material with a simple magnetic structure with two sublattice spins aligned in easy planes and having small in-plane magnetic anisotropy, its critical behavior has not been studied in detail. Here we present an experimental investigation of the critical magnetic field for the transition from the AF to the spin-flop (SF) phase obtained with magnetization and susceptibility measurements. The measured temperature dependence of the AF-SF critical field can be quite well explained by the instability of the low-lying magnon mode with energy renormalized by four-magnon interactions.