Field induced transition in the paramagnetic state of (Sm0.65Sr0.35))MnO3 associated with matnegic clusters

Abstract

The susceptibility of (Sm0.65Sr0.35)MnO3 shows an unusual temperature dependence above the Curie temperature which is attributed to the presence of small manganese-ion clusters with S?9. A field-induced transition is observed in the paramagnetic state, which corresponds to a doubling of the cluster size and an increase of the strength of the interaction between them. The continuous transition from small to large clusters is interpreted in terms of electron phase segregation in a two-phase region. Magnetic hysteresis in the paramagnetic state is ascribed to potential fluctuations due to Sr substitution. Magnetoresistance measurements correlate with the magnetic measurements by showing a change of regime from quadratic to linear in field when the magnetic transition is induced. Thermal hysteresis of about 8 K in the magnetization and resistivity around the Curie temperature (TC=120K) is also related to the existence of the two paramagnetic phases.