Bandwidth-controlled magnetic and electronic transitions inLa0.5Ca0.5−xSrxMnO3(0<~x<~0.5)distorted perovskite

Abstract

We have investigated the effect of the increase of the one-electron e g bandwidth ( W ) on the ferromagnetic and antiferromagnetic transitions in charge ordered La 0.5 Ca 0.5 MnO 3 by substituting bigger Sr 2 + ions for Ca 2 + ions through electrical resistivity and low-field ac-susceptibility measurements as a function of temperature. The system La 0.5 Ca 0.5 − x Sr x MnO 3 is shown to undergo structural transitions with increasing x . For x = 0.0 and 0.1, the structure is orthorhombic with space group Pnma . For x = 0.2 , 0.3, and 0.4, the structure is consistent with a monoclinic space group I 2 / a . The end member ( x = 0.5 ) has a tetragonal structure ( I 4 / m c m ) . T C increases with x monotonically, consistent with the fact that the increase of W enhances double-exchange ferromagnetic interaction. On the other hand, in contrast to the expected monotonic suppression, T N increases initially with Sr concentration, followed by a decrease, finally disappearing for x = 0.4 . The nonmonotonous variation of T N may indicate a possible change in the type of magnetic structure in the antiferromagnetic state.