Effect of progressive substitution of Bi3+ by La3+ on the structural, magnetic, and transport properties of Bi0.6Ca0.4MnO3

Structural, magnetic, and electronic transport properties of Bi0.6-xLaxCa0.4MnO3 (0 <= x <= 0.6) manganites have been studied systematically. The parent compound exhibits robust charge ordered antiferrromagnetic (COAFM) phase with T-CO similar to 293 K and AFM Neel temperature T-N similar to 149 K. The sample with x = 0.1 show a M (T) curve of "arch bridge" form between 142 and 253 K, which is attributed to the AFM peak embedded in the broad transition of the CO. For the middle doping samples (0.2 <= x <= 0.4), although the CO peaks disappear as a result of the suppression of the long range CO state, AFM superexchange coupling has been strengthened with the increasing of La doping level. The Bi0.1La0.5Ca0.4MnO3 sample shows interesting phenomena such as magnetization steps and magnetic memory effect. The resistivity of the samples exhibits insulating behavior in our measured temperature range for x <= 0.4. While both x = 0.5 and x = 0.6 compounds exhibit metal-insulator transition. Furthermore, large low field magnetoresistance (MR) and hysteresis appears only in the MR (H) curve of x = 0.5 sample. These results are discussed in terms of the charge localization caused by the lattice distortion due to the character of the 6s(2) lone pair of Bi3+ ions. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3506683]