Spin cycloid quenching in Nd3 ⁺-substituted BiFeO ₃

Chemical substitution is an effective method for tailoring the electronic and magnetic properties of functional materials. In this work, we employ magneto-optical spectroscopy to investigate the behavior of the cycloid → homogenous ordering transition in Bi _1-xNd _xFeO ₃. From the magneto-optical response, we construct a B-T-x phase diagram that shows how the critical field decreases with Nd3 ⁺ substitution, an effect that we model with Ginzburg-Landau free energy and harmonic cycloid approximations. Compared with nonmagnetic impurities like La3 ⁺, Nd3 ⁺ is a stronger quencher and yields nonlinear B _C-x behavior. Spiral magnetic order is quenched when x∼0.2. With increasing temperature (T<90 K), the critical field rises gently, a consequence of magnetic anisotropy changes with temperature. These findings extend our understanding of charge-spin coupling and advance the development of magnetic ferroelectrics.