Charge/orbital ordering in perovskite manganites

We have studied the phenomena relevant to charge/orbital ordering in perovs kite manganites. In the three bandwidth controlled systems, La-0.7(Sr1-yCay )(0.3)MnO3 (x=0.3), (Nd1-ySmy)(0.55)Sr0.45MnO3 (x=0.45), and Pr-0.65(Sr1-yC ay)(0.35)MnO3 (x=0.35), the variation of the magnetic and electronic proper ties with y has been studied as the hole doping level is kept constant. As y increases (the effective one-electron bandwidth decreases), the colossal magnetoresistance (CMR) or charge /orbital ordering appears. That is, the C MR is caused by competition between double exchange and charge/orbital orde ring. As another issue, the electronic and magnetic properties of the order ed double perovskite Sr2FeMoO6 (T(C)similar to 420 K) have been studied by utilizing single crystals. (C) 2001 Elsevier Science BY. All rights reserve d.