Metamagnetic Phase Transitions in Ceramics

The temperature dependences of ac magnetic susceptibility of the (Sm0.5Gd0.5)0.55Sr0.45MnO3 ceramics provide evidence of the formation of a mixed insulating state with a specific quantum-disordered phase, in which the domains with a long-range antiferromagnetic order dominate at temperatures below N？48,5 K. Irreversible metamagnetic phase transition in the ferromagnetically ordered state is carried out at the critical field c1～25 kOe which remains constant in the temperature range from 4.2 K to 60 K. From the analysis of the magnetization isotherms, the conclusion can be made about a spontaneous phase transition into the state with charge and orbital ordering at temperatures below the critical value CO～60 K. It is supposed that short-range charge correlations exist in unusually large interval of temperatures ~90 K at temperatures above CO that considerably exceeds the area of existence of local orbital correlations ~50 K.