Effect of Bi-doping on structural, magneto-caloric and magneto-resistive properties of La0.67- xBixCa0.33MnO3 perovskites

Abstract

We report the doping effect of Bi on structural, magnetic and magneto-resistive properties of nanocrystalline La0.67-xBixCa0.33MnO3 (x = 0, 0.05, 0.1) (LBCMO) samples. Rietveld refinement of the X-ray diffraction (XRD) patterns revealed that all the three samples crystallize into orthorhombic crystal structure having Pbnm space group. The average crystallite size was calculated using Debye Scherer's formula and the crystallite size varies from 25 to 30 nm. Scanning electron microscopy (SEM) images shows that the particles are spherical in nature and distributed uniformly. The temperature dependent magnetization data infers that all the three samples undergo paramagnetic to ferromagnetic (PM-FM) phase transition with transition temperature (Tc) ~245 K, 250 K and 230 K upon cooling. La0.67Ca0.33MnO3 (LBCMO1), La0.62Bi0.05Ca0.33MnO3 (LBCMO2) samples exhibit second order magnetic phase transition, whereas La0.57Bi0.1Ca0.33MnO3 (LBCMO3) sample exhibit first order like transition. The maximum magnetic entropy changes |ΔSMmax| were calculated for nanocrystalline LBCMO samples using thermodynamic relations and the values were 3.73 Jkg−1K−1, 4.72 Jkg−1K−1 and 4.47 Jkg−1K−1 respectively, where field change was μoH = 5 T. As a consequence of temperature dependence of electrical resistivity, data shows metallic behavior before metal-semiconductor transition temperature (TMS) and semiconducting behavior after TMS. The magnetic field dependent electrical resistivity data reveals a huge change in resistivity near TMS and the maximum magnetoresistance (MR) value around ~60% for an applied field of 5T around the TMS for LBCMO3 sample. The coexistence of magnetocaloric effect and moderately high value of magnetoresistance makes the studied samples promising for multifunctional device applications near its critical temperature.