Sr and Ba substitution in charge ordered Pr_(0.5)Ca_(0.5)MnO_3: Sharp steps in the magnetic and transport properties for a narrow composition range

摘要

The magnetic and transport properties of Pr_(0.5)Ca_(0.5-x)A_x MnO_3 (A = Sr, Ba) have been investigated in this paper. The substitution of Ca with bigger cations such as Sr and Ba can favour the field-induced ferromagnetism and induce sharp steps in the magnetization versus field and resistivity versus field curves. These properties strongly depend on the thermal history of the samples. All the results have been interpreted by a martensitic-like mechanism based on phase separation induced by A-site size mismatch. The above model can also explain the result that the less efficient ability of Sr substitution than Ba substitution to induce ferromagnetism and sharp steps. Another interesting feature in the system is the existence of an optimum substitution range to induce magnetization steps and reach high field-induced magnetization values for both Sr (x = 0.07-0.10) and Ba (x=0.01-0.08) substitution. We suggest that the disappearance of the steps beyond the optimum substitution range possibly results from the different nature of phase separation in the optimum substitution range and beyond this range.