Anomalous magnetic behavior in La2/3Ca1/3MnO3 near the critical point: stable clusters and crossover to uniform ferromagnetism

Abstract A detailed study of the magnetization M(H, T) of bulk ceramic La2/3Ca1/3MnO3 ( T c =267 K) in the paramagnetic phase is presented. Near Tc ( T−T c K ) first-order phase transition features are found. At low magnetic fields (H : 0.3–50 Oe), a sequence of step and plateaus in the effective Curie constant C(T)=M(T−Tc)/H is found, accompanied by temperature hysteresis. At higher fields, maxima in dM/dH are found at a characteristic field, Hc(T), that increases almost linearly with T−Tc up to a critical point ( T c ∗ ≈ 292 K , H c ≈15 kOe ). These features agree with the results of the Landau theory of phase transition with negative M4 coefficient in the energy expansion (for first order). On the other hand, the crossover field between the H2 and classical H2/3 magnetoresistance regimes corresponds closely to Hc(T) near Tc but does not reach an end point at least up to 297 K (32 kOe).