Studies on La0.67Ca0.33MnO3–SrTiO3 composites using two-phase model

In this study we report the structural, electrical and magnetic properties of (1 − x)La0.67Ca0.33MnO3 (LCMO)–(x)SrTiO3(STO) composites. For this series we have observed a minute change in ferromagnetic (FM)–paramagnetic (PM) transition temperature with STO addition in LCMO matrix; however a reasonable change is observed in metal–insulator transition temperature, along with the occurrence of percolation threshold for x = 0.30 sample. Overall pattern for temperature dependence of resistivity for this series has been best-fitted using the formula 1/ρ = (1 − f)/ρPM + (f/ρFM), whereρPM and ρFM are the resistivities of the PM and FM contents in the sample and f is the volume fraction of FM phase in the sample. Investigations on magnetoresistance (MR) using magnetic field up to 3 T show enhancement of extrinsic MR in the composite samples which can be viewed in the light of spin polarized tunneling.

► In this report, we have presented detailed studies on structural, electrical and magnetic behaviours of (1 − x)LCMO–(x)STO composite series. The samples of the present series show TMI < TC, along with the occurrence of percolation threshold for x = 0.30 sample. Very low temperature (<35 K) resistivity behaviour has been analysed using Coulomb blockade model. The overall resistivity data have been successfully fitted by two-phase phenomenological model. Composite samples of this series show purely extrinsic MR behaviour and the highest achieved MR is found to be 41% at 5 K, which is reasonably more compared to previous report [Joshi et al., Phase Transit. 83 (2010) 482].