Effect of Ba doping on structure and magneto-transport properties of layered manganite La1.4Ca1.6-xBaxMn2O7

The magneto-transport properties of the double-layer manganite La1.4Ca1.6-xBaxMn2O7 (LCBMO) (x = 0.0, 0.2, 0.4 and 0.6) have been studied in the temperature range 300-20 K. Polycrystalline bulk samples were prepared by the solid-state reaction route. The X-ray diffraction reveals these samples to be single phased having Sr3Ti2O3-type tetragonal crystal structure. Lattice parameters are found to increase with increasing Ba content. The paramagnetic (PM) to ferromagnetic (FM) transition temperature (T-C) is observed to shift to higher values with the increase in the Ba content and TC values are 135, 144, 163 and 185 K, respectively, for Ba contents x = 0.0, 0.2, 0.4 and 0.6. The increase in the TC may be due to the reduction of the distortion of the MnO6 octahedron and hence suppression of the Jahn-Teller distortion due to substitution of larger Ba cations. The resistivity of all the samples is found to decrease as the temperature is reduced, and below TC an insulator to metal (IM) transition is observed at a temperature T-P which is 125, 131. 133 and 136 K for x = 0.0, 0.2, 0.4 and 0.6, respectively. The increased discrepancy between the T-C and T-P values is due to the increased anisotropy of the FM exchange interaction as a consequence of Ba doping. There is a significant increase (similar to 30% increase) in the low-field low-temperature magnetoresistance in the Ba-doped samples. At 77 K and H-dc = 600 Oe, the magnetoresistance values are measured to be 10, 10.7, 11.5 and 13.2%, respectively x = 0.0, 0.2. 0.4 and 0.6. (c) 2004 Elsevier B.V. All rights reserved.