Abstract
Polycrystalline La1-x Pb x MnO3±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 (β, γ and δ) 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.
Highlights
The perovskite manganite oxides have been studied extensively for their colossal magnetoresistance [1], Jahn–Teller (J–T) distortions [2], metal–insulator transitions [3] and most importantly the strong coupling between lattice, charge, orbit and spin degrees of freedom [4]
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 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
Summary
The perovskite manganite oxides have been studied extensively for their colossal magnetoresistance [1], Jahn–Teller (J–T) distortions [2], metal–insulator transitions [3] and most importantly the strong coupling between lattice, charge, orbit and spin degrees of freedom [4]. Owing to their chemical stability, low-cost synthesis, zero field-hysteresis and. With critical scaling analysis (using intrinsic magnetic field in the analysis), the type of critical behaviour in the LPMO samples have been determined and compared with theoretical models. To the best of our knowledge, this is the first report of the evolution of the GP in the Pb-substituted LaMnO3 system
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