Enhanced magnetocaloric effect with the high tunability of bismuth in La0.8Na0.2Mn1-xBixO3 (0 ≤ x ≤ 0.06) perovskite manganites

In this paper, we have reported in details the effect of bismuth doping on the structural, magnetic and magnetocaloric properties of the nominal composition La0.8Na0.2Mn1-xBixO3 (0 <= x <= 0.06). All the compounds were synthesized by using the conventional solid-state reaction with a final sintering temperature of 1400 degrees C. For the undoped compound, the X-ray refinement shows the coexistence of two phases: a major phase crystallizing in the rhombohedral structure with R-3C space group and a minor one corresponding to Mn3O4, which adopts the tetragonal symmetry with 141/amd space group. However, the doped compounds (x = 0.03 and x = 0.06) are only indexed in the rhombohedral structure with R-3C space group without the presence of any minor phase. M(T) and M(H) investigations show a single ferromagnetic-paramagnetic transition with increasing temperature. The Curie temperature values decrease gradually with Bismuth doping, 330 K for x = 0, 320 K for x = 0.03, and 310 K for x = 0.06. Moreover, a wide variation in the magnetic entropy change with respect to temperature has been noticed and it indicates a significant magnetocaloric effect. The maximums of the magnetic entropy change -Delta S-M at mu H-0 = 5T are 4.73 J/Kg K, 4.77 J/Kg K and 5.20 J/Kg K for x = 0, 0.03 and 0.06 at 335 K, 325 K and 315 K, respectively. The RCP values of our current compounds are 241 J Kg(-1), 218 J Kg(-1) and 229 J Kg(-1) with negligible hysteresis losses, thus offering the opportunity to use them in the magnetic refrigeration. The master curve investigations display the collapse of the entire curves in the same plot to convey the second order transition of the compounds. (C) 2017 Elsevier B.V. All rights reserved.