Ghorai Sagar, Ivanov Sergey, Skini Ridha, Svedlindh Peter
Uppsala Universitet, Ångströmlaboratoriet, Lägerhyddsvägen 1, 751 03 Uppsala, Sweden, Uppsala, 751 03, SWEDEN.
Solid State Physics Angstrom Laboratory, Uppsala University, Box 35, SE-751 03, Uppsala, 75103, SWEDEN.
J Phys Condens Matter. 2021 Jan 19. doi: 10.1088/1361-648X/abdd64.
Polycrystalline LaPbMnO(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 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 ferromagnetic clusters. Long-range ferromagnetic order is established as the result of long-range interactions between ferromagnetic 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 at 5 T field) and a magnetic phase transition near room temperature.
采用固态反应法制备了多晶LaPbMnO（x = 0.3、0.35、0.4）固溶体，并对其磁性能进行了研究。X射线粉末衍射图谱的Rietveld精修表明，所有样品均为单相，且在R-3c空间群中以菱面体结构结晶。所有材料均观察到二级顺磁到铁磁相变。通过反磁化率的温度依赖性确定的格里菲斯相（GP），会因磁场增加而受到抑制，并且对A位化学取代表现出显著依赖性。利用本征磁场数据，在居里温度附近研究了这些化合物的临界行为。对于所有三种化合物，临界指数（β、γ和δ）均接近平均场近似值。观察到的类似平均场行为是GP和铁磁团簇形成的结果。铁磁团簇之间的长程相互作用导致了长程铁磁序的建立。从等温熵变的角度研究了磁热效应。我们的研究表明，化学取代最低（x = 0.3）的材料（在这三种化合物中）作为磁制冷材料具有最高潜力，这归因于其较高的相对制冷功率（在5 T磁场下为258 J/kg）以及接近室温的磁相变。
