Role of intergrowths in the properties of naturally layered manganite single crystals

Two-layered Ruddlesden-Popper phase SrO(La1-xSrxMnO3)(2), with x = 0.3 and 0.3, exhibits colossal magnetoresistance, a magnetic anisotropy which is strongly composition-dependent, very little remanence, and an anomalous low-field magnetization (M) plateau between the Curie temperature (T-C) and T* similar to 300 K. The resistivity peaks near T-C for both in-plane and out-of-plane currents. The magnetization plateau is not intrinsic to the crystal, but is attributed to intergrowth defects, consisting of one additional or missing SrO blocking layers, as observed in transmission electron micrographs. The intergrowths exhibit interesting two-dimensional magnetic behavior, for both the x = 0.3 and 0.3 compositions. For x = 0.4, M scales as (1 - T/T*)(beta), with beta = 0.25 +/-0.02, For x = 0.3, the intergrowths exhibit an easy axis in the a-b plane due to the shape anisotropy, while for T<T-C, M lies along the c axis. (C) 1998 American Institute of Physics. [S0021-8979(98)43311-5].