Antiferromagnetic resonance in charge ordering state of Pr _0.5Ca_0.5MnO_3-δ single crystal

An antiferromagnetic resonance (AFMR) is observed in the charge ordered antiferromagnetic phase of Pr_0.5Ca_0.5MnO _3-δ single crystal for the first time. Above the Néel temperature, T_N = 173 K, a paramagnetic resonance with g = 2.0 is observed, There is no significant change of the resonance spectra at the charge ordering transition temperature, T_co = 242K, Below T_N, a branch of AFMR is found. Since the resonance field of this mode increases linearly as the frequency is decreased, this branch is assigned, as the spin-flop mode. Below 60K, the critical fields, B_c, evaluated as the extrapolation of this mode to zero frequency agree well with the insulator-metal transition fields, B_CO, at which the melting of the charge-ordering phase occurs. Present results indicate that the temperature dependence of B _co is affected by the temperature dependence of Bc.