Electrical, magnetic and magnetocaloric properties of selected b-site substituted manganites

Abstract

The objective of the present work is to study the influence of impurity doping at Mn-site in charge ordered (CO) manganites, on the destruction of CO state and other physical properties, i.e. structural, electrical, magnetic and magnetothermal properties, with an emphasis on magnetocaloric effect. A systematic study has been carried out for the CO insulating system, Pr0.6Ca0.4MnO3 by substituting different elements (Cr, Co, Ni, Ru, Fe and Al) at Mn site. This study essentially revealed that long range ferromagnetism and metallic behavior are induced only for the impurities Cr, Co, Ni and Ru but Fe and Al substitutions made the compound remain antiferromagnetic insulator. From the magnetization isotherms and direct calorimetric measurements it has been observed that Co doped sample exhibits maximum value of magnetocaloric effect, -7.37 J/kg K followed by Ni, Cr and Ru. It has been found that the applied magnetic field induces a metamagnetic transition above Curie temperature in Co, Ni and Cr substituted samples but not in that of Ru substituted compound that has the lowest resistivity and highest TC. These differences were argued in the light of existence of CO fluctuations and ferromagnetic polarons in the paramagnetic phase of Co, Ni and Cr samples. We have further extended this study in case of Bi based charge ordered compounds which are known for their more robust charge ordering.