Influence of Na Addition on Magnetic and Magnetocaloric Effects of La0.67Pb0.13Na0.2MnO3 Ceramics

Structural, magnetic, magnetocaloric, and electrical properties are reported for mixed-valence manganite La_0.67Pb_0.13Na_0.2MnO₃. X-ray diffraction reveals that the sample crystallizes in the rhombohedric structure with the R-3c space group. The magnetic properties of the polycrystalline La_0.67Pb_0.13Na_0.2MnO₃ compound are discussed in detail, based on the susceptibility, magnetization, and isotherm. The sample presents a ferromagnetic property with T _C= 275 K and a Griffiths phase at T _G= 325 K which gives the existence of ferromagnetic clusters in the paramagnetic domain. A large deviation is usually observed between field cooled (FC) and zero field cooled (ZFC). M(T) is a low temperature below the blocking temperature. At 40 K, a spin-glass or a cluster-glass state is seen to arise from a ferromagnetic state. This is caused by the competition between the antiferromagnetic and ferromagnetic interactions. The electrical properties show the presence of a metal–semiconductor transition at T _M?Sc. To understand the dependence of disorder with the transport mechanism, we used the phenomenological equation for resistivity under a percolation approach, which is dependent on the phase segregation of a paramagnetic semiconductor and ferromagnetic metallic regions.