Canted spin structure in clusters of the (La 0.7Ca 0.3) 1− xMn 1+ xO 3 perovskites

Abstract

In this paper, we report on the effect of excess manganese on the magnetic properties of the (La 0.7Ca 0.3) 1− x Mn 1+ x O 3 perovskites. All samples display a colossal magnetoresistance effect which becomes considerably enhanced with increasing manganese content. The magnetic behaviour of manganites studied was shown to depend strongly on the values of manganese doping and applied magnetic field. For the samples with x=0.1 and 0.2, in addition to an anomaly connected with paramagnet–ferromagnet transition, there are anomalies in the field-cooled (FC) and zero-field-cooled (ZFC) magnetization at low temperatures. In low magnetic fields ( H<150 Oe), the M FC( T) curves have a kink near T C, and the FC and ZFC magnetization drop appears below 45 K. In applied fields of H>200 Oe, a jump upwards takes place in the M FC( T) and M ZFC( T) curves at the same temperature. A low-temperature anomaly in AC susceptibility also indicates a change in magnetic ordered state. From M( T, H) and χ( T) dependencies, one can assume the existence of regions with different magnetic order at T<45 K: a main part of the sample being a ferromagnetically ordered one and a minor one being a noncollinear state. The latter is most probably to present mesoscopic inhomogeneity containing clusters with canted spin structure. The large irreversibility in the FC and ZFC magnetization arises due to the blocking of cluster magnetic moment below T C.