Nonanalyticity of magnetization curve for Dzialoshinsky-Moriya antiferromagnet: LaMnO3 as a model magnet

An extensive study of the energy expression for an antiferromagnetic system with antisymmetric Dzialoshinsky-Moriya (DM) interaction and uniaxial magnetocrystalline anisotropy is presented and the main features are shown as a function of magnetic field H applied along the different crystallographic directions. The spin-flop transition is analyzed showing that for DM coupling constant DD_crit the transition changes from first to second order. Analytical results are followed by numerical computer simulations, both for single crystal and for polycrystal with isotropic easy axis distribution. First and second derivative of the average magnetization with respect to H are analyzed as well, for their insight potentiality: the first derivative is found to be useful for a direct measurement of the spin-flop transition field in polycrystalline samples, while the shape of the second derivative allows us to distinguish the case D0 from the case D