Chemical control of colossal magnetoresistance in manganites

The evolution of the structural, electrical and magnetic properties with th e isovalent chemical substitution of Ca2+ into the Sr2+ sites in the new se ries of two-dimensional La-1.2 (Sr1.8-x Ca-x)Mn2O7 samples (0 less than or equal to x less than or equal to 0.8) and three-dimensional La-0.6(Sr0.4-xC ax)MnO3 samples (0 < x < 0.4) has been investigated. The compositional depe ndence of the structural variation has been found in La-0.6(Sr0.4-x Ca-x)Mn O3. The Curie temperatures (T-C) decreased from 135 to 102 K and 370 to 270 K for x = 0-0.4 in La-1.2(Sr1.8-x Ca-x) Mn2O7 and La-0.6 (Sr0.4-xCax) MnO3 , respectively. Our results confirm that the dimensionality as well as ioni c size plays an important role in controlling the colossal magnetoresistanc e in manganites. (C) 2001 Elsevier Science B.V. All rights reserved.