DOI: https://doi.org/10.55373/mjchem.v25i3.164

Keywords: Manganites; doping; structural; magnetic; electrical

Abstract

The discovery of colossal magnetoresistance (CMR) effect on manganite has led to increased attention to explore the main properties of these materials. A review study was conducted to understand the influence of ‘A’ site doping on lanthanum (La)-based manganites and evaluate their structural, magnetic and electrical properties. In general, lanthanum, a rare earth element, can be used to create La1-xAxMnO3, where A represents monovalent ions (Na, K or Ag) or divalent ions (Ba, Pb, Sr or Ca) that are octahedrally coordinated by oxygen ions. This work also discusses the structure, phase diagram, double-exchange mechanism and phase separation of CMR manganites. La-based parent compounds doped at the A site (Na, K, Ba, Sr) were synthesised by a conventional solid-state method. When x increases, the CMR increases due to the competition between charge ordering and double exchange. At high temperatures or high applied magnetic fields, manganites exhibit extraordinarily large CMR in response to the transition of insulator–metal and paramagnetic–ferromagnetic regions at the same temperature. The substitutions of A doping could increase the lattice distortion between the ions and cause size mismatch. The electrical resistivity results reveal that manganites act as an insulator behaviour at above the metal–insulator transition temperature TMI and as metal at below TMI. The resistivity increases when the A site concentration in the compound increases.