Evolution of Griffiths phase and critical behaviour of La1-xPbxMnO3±y solid solutions

Polycrystalline La1-xPbxMnO3 +/- y (x = 0.3, 0.35, 0.4) solid solutions were prepared by solid state reaction method and their magnetic properties have been investigated. Rietveld refinement of x-ray powder diffraction patterns showed that all samples are single phase and crystallized with the rhombohedral structure in the R-3c space group. A second order paramagnetic to ferromagnetic (FM) phase transition was observed for all materials. The Griffiths phase (GP), identified from the temperature dependence of the inverse susceptibility, was suppressed by increasing magnetic field and showed a significant dependence on A-site chemical substitution. The critical behaviour of the compounds was investigated near to their Curie temperatures, using intrinsic magnetic field data. The critical exponents (beta, gamma and delta) are close to the mean-field approximation values for all three compounds. The observed mean-field like behaviour is a consequence of the GP and the formation of FM clusters. Long-range FM order is established as the result of long-range interactions between FM clusters. The magnetocaloric effect was studied in terms of the isothermal entropy change. Our study shows that the material with the lowest chemical substitution (x = 0.3) has the highest potential (among the three compounds) as magnetic refrigerant, owing to its higher relative cooling power (258 J kg(-1) at 5 T field) and a magnetic phase transition near room temperature.

Automated summary

Polycrystalline La1-xPbxMnO3 +/- y solid solutions prepared by solid state reaction exhibit unique magnetic properties, with a second order paramagnetic to ferromagnetic phase transition and suppression of the Griffiths phase. The compounds show mean-field like behavior near their Curie temperatures, resulting from the formation of ferromagnetic clusters. The material with the lowest chemical substitution (x = 0.3) shows the highest potential as a magnetic refrigerant due to its higher relative cooling power and magnetic phase transition near room temperature.