Influence of sintering time on the magnetoresistance properties of bulk La1-x-yCaxSryMnO3

Abstract

The Lal.,.vCa,SryMnO) powders with various x and y values were synthesized using a standard ceramic technique. Powders of LazO) (Aldrich 99.99%), CaC03 (BOH 999%), SrC01 (BOI-I 99.9%) and MnzO) (Aldrich 99.9%) were used to make the required composition. The ingredients were weighed with appropriate proportions and then mixed thoroughly in dry and acetone media. Four different compositions were prepared for different x and y values keeping their sum 0.30. The mixed powders were calcined at 950°C for 24 hours. After calcination powders were pressed in the form of pellets. The pellets of four different compositions were sintered at 1200°C for various dwell times (60h, 40h, 20h and 12h). X-ray diffraction was carried out in the powder sample for structural characterization. Electrical resistance were measured in each sample in zero field and in presence applied magnetic field (0.60 T) in the temperature range 295-77K. It was observed that all samples show metal-insulator transition at certain temperature (Tp). Metal-insulator transition temperature varies for different compositions. It was observed that as the Sr concentration increases in the polycrystalline LaJ.,.yCa,SryMnO).o samples the 1;' increases. Magnetoresistance (MR) as a function field, MR(H), at constant temperatures (77 K and room temperature) were measured. All samples show non-trivial MR at RT and at 77K. It was found that the MR at 77K is higher for the sample sintered for lower dwell time. For all samples MR at 77K showed two slopes. A sharp decrease of resistance is observed up to applied field H'. Beyond H' resistance has a weak dependence in applied field. The sharp decrease of resistance is due to the domain wall movement and the weak dependence is related to the grain boundaries of the polycrystalline samples. The LU(17oCaoIOSrzoMn03-<i.sample sintered at 1200°C for 40h shows 3% MR at RT in presence of 0.61' applied field. The polycrystalline sample of nominal chemical composition Lao.7oCao.IOSr20MnO)-a<lsio has highest 1;' (279K).