Anomalous low-field magnetization in La2/3Ca1/3MnO3 near the critical point:: Stable clusters?

The magnetic behavior of bulk La2/3Ca1/3MnO3 (T-C = 267 K) at low fields in the paramagnetic phase was studied, Near T-C(T- T-C<30 K) we find a sequence of steplike features in the effective Curie constant C(T)=M(T-T-C)/H at well defined temperatures and intermediate plateaus, accompanied by temperature hysteresis. On approaching T-C, the C values at each plateau follow a geometrical progression, with the effective spin S doubled at each step, The first plateau gives S = 5,5, corresponding to a cluster of three Mn3+ ions sharing one extra hole, This suggests that close to T-C short range magnetic order at low fields develops hierarchically through a series of most stable cluster states, (C) 1998 American Institute of Physics. [S0021-8979(98)52311-0].