Disorder effects in (LaTb)0.5(CaSr)0.5MnO3 compounds

Electrical, magnetotransport, and magnetization measurements have been carried out on half-doped (La0.5-xTbx)(Ca0.38-ySr0.12+y)MnO3 (0.025less than or equal toxless than or equal to0.125; y=0.8x) compounds. The increase in Tb3+ and Sr2+ contents keeps the average A-site ionic radius constant at similar to1.215 Angstrom but introduces increasing size disorder. The insulator-metal transition temperature (T-p) falls from 191 to 107 K and the Curie temperature (T-C) falls from 230 to 106 K as x increases from 0.025 to 0.125. Interestingly, with increasing size disorder, the disparity between T-C and T-p disappears and magnetoresistance increases around T-p but decreases at low temperatures. This is discussed in the light of phase segregation. (C) 2004 American Institute of Physics.